菜豆ANK基因家族鉴定及ANK25的表达模式分析

锚蛋白重复序列模体是生物体内最普遍的蛋白质序列模体之一,在多种细胞活动中主要介导蛋白质-蛋白质的相互作用。本研究利用菜豆基因组数据库,通过生物信息学手段对菜豆ANK家族成员及分子生物学特性进行了鉴定。结果显示,菜豆基因组中含有30个ANK家族基因,分布于9条染色体上,其中第5条染色体上含有的ANK基因最多,包含13个基因。蛋白结构域分析发现,ANK25除了含有ANK结构域外还含有RING结构域。亚细胞定位结果显示,ANK25主要分布在细胞膜上。表达模式分析发现,ANK25对干旱、盐和ABA胁迫有响应。本研究为进一步研究菜豆ANK的分类及功能提供了有利的依据。     

Structure-based substitutions for increased solubility of a designed protein

Manipulation of protein solubility is important for many aspects of protein design and engineering. Previously, we designed a series of consensus ankyrin repeat proteins containing one, two, three and four identical repeats (1ANK, 2ANK, 3ANK and 4ANK). These proteins, particularly 4ANK, are intended for use as a universal scaffold on which specific binding sites can be constructed. Despite being well folded and extremely stable, 4ANK is soluble only under acidic conditions. Designing interactions with naturally occurring proteins requires the designed protein to be soluble at physiological pH. Substitution of six leucines with arginine on exposed hydrophobic patches on the surface of 4ANK resulted in increased solubility over a large pH range. Study of the pH dependence of stability demonstrated that 4ANK is one of the most stable ankyrin repeat proteins known. In addition, analogous leucine to arginine substitutions on the surface of 2ANK allowed the partially folded protein to assume a fully folded conformation. Our studies indicate that replacement of surface-exposed hydrophobic residues with positively charged residues can significantly improve protein solubility at physiological pH.     

Sequential unfolding of ankyrin repeats in tumor suppressor p16

The ANK repeat is a ubiquitous 33-residue motif that adopts a beta hairpin helix-loop-helix fold. Multiple tandem repeats stack in a linear manner to produce an elongated structure that is stabilized predominantly by short-range interactions between residues close in sequence. The tumor suppressor p16(INK4) consists of four repeats and represents the minimal ANK folding unit. We found from Phi value analysis that p16 unfolded sequentially. The two N-terminal ANK repeats, which are distorted from the canonical ANK structure in all INK4 proteins and which are important for functional specificity, were mainly unstructured in the rate-limiting transition state for folding/unfolding, while the two C-terminal repeats were fully formed. A sequential unfolding mechanism could have implications for the cellular fate of wild-type and cancer-associated mutant p16 proteins.     

The ASPP interaction network: electrostatic differentiation between pro‐ and anti‐apoptotic proteins

The ASPP proteins are apoptosis regulators: ASPP1 and ASPP2 promote, while iASPP inhibits, apoptosis. The mechanism by which these different outcomes are achieved is still unknown. The C‐terminal ankyrin repeats and SH3 domain (ANK‐SH3) mediate the interactions of the ASPP proteins with major apoptosis regulators such as p53, Bcl‐2, and NFκB. The structure of the complex between ASPP2_ANK‐SH3 and the core domain of p53 (p53CD) was previously determined. We have recently characterized the individual interactions of ASPP2_ANK‐SH3 with Bcl‐2 and NFκB, as well as a regulatory intramolecular interaction with the proline rich domain of ASPP2. Here we compared the ASPP interactions at two levels: ASPP2_ANK‐SH3 with different proteins, and different ASPP family members with each protein partner. We found that the binding sites of ASPP2 to p53CD, Bcl‐2, and NFκB are different, yet lie on the same face of ASPP2_ANK‐SH3. The intramolecular binding site to the proline rich domain overlaps the three intermolecular binding sites. To reveal the basis of functional diversity in the ASPP family, we compared their protein‐binding domains. A subset of surface‐exposed residues differentiates ASPP1 and ASPP2 from iASPP: ASPP1/2 are more negatively charged in specific residues that contact positively charged residues of p53CD, Bcl‐2, and NFκB. We also found a gain of positive charge at the non‐protein binding face of ASPP1/2, suggesting a role in electrostatic direction towards the negatively charged protein binding face. The electrostatic differences in binding interfaces between the ASPP proteins may be one of the causes for their different function. Copyright © 2010 John Wiley & Sons, Ltd.     

Structure Function Studies of Vaccinia Virus Host Range Protein K1 Reveal a Novel Functional Surface for Ankyrin Repeat Proteins

Poxvirus host tropism at the cellular level is regulated by virus-encoded host range proteins acting downstream of virus entry. The functioning mechanisms of most host range proteins are unclear, but many contain multiple ankyrin (ANK) repeats, a motif that is known for ligand interaction through a concave surface. We report here the crystal structure of one of the ANK repeat-containing host range proteins, the vaccinia virus K1 protein. The structure, at a resolution of 2.3 Å, showed that K1 consists entirely of ANK repeats, including seven complete ones and two incomplete ones, one each at the N and C terminus. Interestingly, Phe82 and Ser83, which were previously shown to be critical for K1''s function, are solvent exposed and located on a convex surface, opposite the consensus ANK interaction surface. The importance of this convex surface was further supported by our additional mutagenesis studies. We found that K1''s host range function was negatively affected by substitution of either Asn51 or Cys47 and completely abolished by substitution of both residues. Cys47 and Asn51 are also exposed on the convex surface, spatially adjacent to Phe82 and Ser83. Altogether, our data showed that K1 residues on a continuous convex ANK repeat surface are critical for the host range function, suggesting that K1 functions through ligand interaction and does so with a novel ANK interaction surface.Poxviruses are large DNA viruses that dedicate a significant portion of their coding capacity for modulating the host antiviral responses, thereby creating a suitable environment for viral replication (9). They encode so-called host range proteins, which are required for their replication in some but not all cell types, presumably because these proteins modulate some cell type-specific antiviral responses (14, 34). K1 and C7 are two critical host range proteins that are encoded by vaccinia virus (VACV), the prototypical orthopoxvirus (22). The deletion of both K1L and C7L genes from VACV results in abortive replication of the mutant in many mammalian cells and severe attenuation in mice (6, 8, 15, 24). In most mammalian cells, K1, C7, and the cowpox virus CP77 proteins function as equivalent host range factors, since any one of the three could rescue the replication defect of ΔK1LΔC7L VACV mutant (24). A notable exception is rabbit kidney RK13 cells, where either K1 or CP77 could rescue the mutant but C7 could not (24). The mechanism by which K1/C7/CP77 facilitate VACV replication in mammalian cells is unclear. Both K1 and CP77 were found to inhibit the activation of NF-κB in response to VACV infection (3, 27). However, inhibition of host NF-κB activation is neither necessary nor sufficient for the function of CP77 as the host range factor (3). More recently, K1 and C7 were found to antagonize antiviral activities induced by type I interferons, and this function of K1 appears to correlate with its function as host range factor (16).Many poxvirus host range proteins, including K1 and CP77, contain multiple ankyrin (ANK) repeats, a 33-residue motif that is only known for a function in protein-protein interactions (26). Recently, a 68-kDa protein that is highly conserved in all orthopoxviruses was found to be a host range factor for VACV strain MVA, and it is the only ANK repeat protein that is preserved in MVA (29, 30). Besides orthopoxvirses, many other vertebrate poxviruses also encode multiple ANK repeat proteins (18), some of which are known to be host range factors. For example, the rabbit specific myxoma virus encodes four ANK repeat proteins, and one of them, M-T5, is a well-characterized myxoma host range factor (33). A hallmark for the majority of the poxvirus ANK repeat proteins is the presence of a unique C-terminal F-box-like motif, which interacts with Skp1 and Cullin-1 of the host SCF ubiquitin ligase complex (28).ANK motif is rarely encountered in viral proteins except the poxvirus proteins, but it is quite common in eukaryotic proteins (21, 26). The 33-residue ANK motif forms a very conserved secondary and tertiary structure, which consists of a canonical helix-loop-helix-β-hairpin/loop fold. The two helices are arranged in an antiparallel mode and followed by a loop region that points outward at a nearly 90° angle. The loop forms a β-hairpin in some cases. Multiple repeats are packed together to form an elongated L-shape structure with a large solvent-accessible surface. The ANK repeat is a very versatile scaffold for creating protein domains displaying specific binding surfaces. Different ANK proteins stack various numbers of the repeats and contain variable surface residues at the repeats, performing diverse biological functions by interacting specifically with their targets (13, 21, 26).To date, in all determined protein complex structures containing ANK repeat proteins, the interaction occurs through a concave surface formed by the β turn and the first α-helix (1, 13, 21, 26). These residues are positioned at the tip of the β turn and along the exposed surface of the first α helix. However, it is unclear whether poxvirus ANK repeat proteins function similarly. Previously, we performed a mutagenesis study of K1 and identified several residues at the second α-helix of a predicted ANK repeat to be critical for its host range function (17). In the present study, we resolved the crystal structure of K1 at 2.3 Å, which represents the first structure of a viral ANK repeat protein. We found that K1 consists entirely of ANK repeats, lacking any F-box. Furthermore, we performed additional mutagenesis study of K1 and identified residues at the second α-helix of another K1 ANK repeat to be critical for K1''s function. In contrast to all previously characterized ANK repeat proteins, the critical K1 residues are all exposed on the convex surface of ANK repeats, suggesting that K1 uses a novel protein-binding mode for its function.     

Two C-terminal ankyrin repeats form the minimal stable unit of the ankyrin repeat protein p18INK4c

Ankyrin repeat proteins (ARPs) appear to be abundant in organisms from all phyla, and play critical regulatory roles, mediating specific interactions with target biomolecules and thus ordering the sequence of events in diverse cellular processes. ARPs possess a non-globular scaffold consisting of repeating motifs named ankyrin (ANK) repeats, which stack on each other. The modular architecture of ARPs provides a new paradigm for understanding protein stability and folding mechanisms. In the present study, the stability of various C-terminal fragments of the ARP p18^INK4c was investigated by all-atomic 450 ns molecular dynamics (MD) simulations in explicit water solvent. Only motifs with at least two ANK repeats made stable systems in the available timescale. All smaller fragments were unstable, readily losing their native fold and α-helical content. Since each non-terminal ANK repeat has two hydrophobic sides, we may hypothesize that at least one hydrophobic side must be fully covered and shielded from the water as a necessary, but not sufficient, condition to maintain ANK repeat stability. Consequently, at least two ANK repeats are required to make a stable ARP. Figure Structure of the p18INK4c protein (PDB entry 1IHB, chain B), which is a member of the cyclin-dependent kinase inhibitor (INK) tumor suppressor family with five ankyrin (ANK) repeat modules. The figure was generated by PyMol Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Distribution, expression, and motif variability of ankyrin domain genes in Wolbachia pipientis

The endosymbiotic bacterium Wolbachia pipientis infects a wide range of arthropods, in which it induces a variety of reproductive phenotypes, including cytoplasmic incompatibility (CI), parthenogenesis, male killing, and reversal of genetic sex determination. The recent sequencing and annotation of the first Wolbachia genome revealed an unusually high number of genes encoding ankyrin domain (ANK) repeats. These ANK genes are likely to be important in mediating the Wolbachia-host interaction. In this work we determined the distribution and expression of the different ANK genes found in the sequenced Wolbachia wMel genome in nine Wolbachia strains that induce different phenotypic effects in their hosts. A comparison of the ANK genes of wMel and the non-CI-inducing wAu Wolbachia strain revealed significant differences between the strains. This was reflected in sequence variability in shared genes that could result in alterations in the encoded proteins, such as motif deletions, amino acid insertions, and in some cases disruptions due to insertion of transposable elements and premature stops. In addition, one wMel ANK gene, which is part of an operon, was absent in the wAu genome. These variations are likely to affect the affinity, function, and cellular location of the predicted proteins encoded by these genes.     

Crystal structure of a 12 ANK repeat stack from human ankyrinR

Ankyrins are multifunctional adaptors that link specific proteins to the membrane-associated, spectrin- actin cytoskeleton. The N-terminal, 'membrane-binding' domain of ankyrins contains 24 ANK repeats and mediates most binding activities. Repeats 13-24 are especially active, with known sites of interaction for the Na/K ATPase, Cl/HCO(3) anion exchanger, voltage-gated sodium channel, clathrin heavy chain and L1 family cell adhesion molecules. Here we report the crystal structure of a human ankyrinR construct containing ANK repeats 13-24 and a portion of the spectrin-binding domain. The ANK repeats are observed to form a contiguous spiral stack with which the spectrin-binding domain fragment associates as an extended strand. The structural information has been used to construct models of all 24 repeats of the membrane-binding domain as well as the interactions of the repeats with the Cl/HCO(3) anion exchanger and clathrin. These models, together with available binding studies, suggest that ion transporters such as the anion exchanger associate in a large central cavity formed by the ANK repeat spiral, while clathrin and cell adhesion molecules associate with specific regions outside this cavity.     

The regulatory role of CD45 on rat NK cells in target cell lysis.

To investigate the role of CD45 in rat NK cell function, we developed new mAbs directed against rat CD45. mAb ANK12 binds to a high molecular isoform of CD45 and mAb ANK74 binds to the common part on all known CD45 isoforms, as has been described for the anti-rat CD45 mAb OX1. The ability of these mAbs to affect NK cell-mediated lysis was tested using the Fc receptor-positive target cell line P815. mAb ANK12 was found to significantly enhance the lysis of P815, whereas ANK74 and the anti-CD45 mAb OX1 did not. In addition, cross-linking of the CD45 isoform by ANK12 induced tyrosine phosphorylation of specific proteins in NK cells. Subsequently, the involvement of CD45 in the negative signaling after "self" MHC class I recognition by rat NK cells was investigated. The anti-CD45 mAbs were found to affect NK cell-mediated lysis of syngeneic tumor cell lines, depending upon the expression level of MHC class I on target cells. mAbs ANK74 and OX1 only inhibited lysis of the syngeneic tumor cell lines that expressed low levels of MHC class I. Furthermore, both mAbs caused an inhibition of NK cell-mediated lysis of these tumor cell lines when MHC class I molecules on the tumor cell lines were masked by an Ab. These results suggest that CD45 regulates the inhibitory signal pathway after self MHC class I recognition, supposedly by dephosphorylation of proteins.     

Identification of Gasz,an evolutionarily conserved gene expressed exclusively in germ cells and encoding a protein with four ankyrin repeats,a sterile-alpha motif,and a basic leucine zipper

To discover causes of infertility and potential contraceptive targets, we used in silico subtraction and genomic database mining to identify conserved genes with germ cell-specific expression. In silico subtraction identified an expressed sequence tag (EST) present exclusively in a newborn mouse ovary library. The full-length cDNA sequence corresponding to this EST encodes a novel protein containing four ankyrin (ANK) repeats, a sterile-alpha motif (SAM), and a putative basic leucine zipper (bZIP) domain. Northern blot and semiquantitative RT-PCR analyses demonstrated that the mRNA is exclusively expressed in the mouse testis and ovary. The expression sites were localized by in situ hybridization to pachytene spermatocytes in the testis and oocytes in the ovary. Immunohistochemistry showed that the novel protein is localized to the cytoplasm in pachytene spermatocytes and early spermatids, oocytes at all stages of oogenesis, and in early preimplantation embryos. Based on its germ cell-specific expression and the presence of ANK, SAM, and basic leucine zipper domains, we have termed this novel protein GASZ. The mouse Gasz gene, which consists of 13 exons and spans 60 kb, is located on chromosome 6 between the Wnt2 and cystic fibrosis transmembrane conductance regulator (Cftr) genes. Using genomic database mining, orthologous genes encoding GASZ were identified in the rat, cow, baboon, chimpanzee, and human. Phylogenetic analyses reveal that the GASZ proteins are highly conserved among these species. Human and mouse GASZ proteins share 85.3% amino acid identity, and human and chimpanzee GASZ proteins differ by only 3 out of 475 amino acids. In humans, the GASZ gene resides on chromosome 7 and is similarly composed of 13 exons. Because both ANK repeats and the SAM domain function as protein-protein interaction modules that mediate signal transduction cascades in some systems, GASZ may represent an important cytoplasmic signal transducer that mediates protein-protein interactions during germ cell maturation in both males and females and during preimplantation embryogenesis.     

Protein profiling of microdomains purified from renal cell carcinoma and normal kidney tissue samples

Renal cell carcinoma (RCC) is representing about 3% of all adult cancers. A promising strategy for cancer biomarker discovery is subcellular comparative proteomics, allowing enriching specific cell compartments and assessing differences in protein expression patterns. We investigated the proteomic profile of a peculiar RCC subcellular compartment, plasma membrane microdomains (MD), involved in cell signalling, transport, proliferation and in many human diseases, such as cancer. Subcellular fractions were prepared by differential centrifugation from surgical samples of RCC and adjacent normal kidney (ANK). MD were isolated from plasma-membrane-enriched fractions after Triton X-100 treatment and sucrose density gradient ultracentrifugation. MD derived from RCC and ANK tissues were analyzed after SDS-PAGE separation by LC-ESI-MS/MS. We identified 93 proteins from MD isolated from RCC tissue, and 98 proteins from ANK MD. About 70% of the identified proteins are membrane-associated and about half of these are known as microdomain-associated. GRAVY scores assignment shows that most identified proteins (about 70%) are in the hydrophobic range. We chose a panel of proteins to validate their differential expression by WB. In conclusion, our work shows that RCC microdomain proteome is reproducibly different from ANK, and suggests that mining into such differences may support new biomarker discovery.     

Differential proteomic analysis of renal cell carcinoma tissue interstitial fluid

Renal cell carcinoma (RCC), the most common type of kidney cancer, currently has no biomarker of clinical utility. The present study utilized a mass spectrometry-based proteomics workflow for identifying differentially abundant proteins in RCC by harvesting shed and secreted proteins from the tumor microenvironment through sampling tissue interstitial fluid (TIF) from radical nephrectomies. Matched tumor and adjacent normal kidney (ANK) tissues were collected from 10 patients diagnosed with clear cell RCC. One-hundred thirty-eight proteins were identified with statistically significant differential abundances derived by spectral counting in tumor TIF when compared to ANK TIF. Among those proteins with elevated abundance in tumor TIF, nicotinamide n-methyltransferase (NNMT) and enolase 2 (ENO2) were verified by Western blot and selected reaction monitoring (SRM). The presence of ENO2 and thrombospondin-1 (TSP1) were verified as present and at elevated abundance in RCC patient serum samples as compared to a pooled standard control by enzyme-linked immunosorbent assay (ELISA), recapitulating the relative abundance increase in RCC as compared with ANK TIF.     

Expression and localisation of the pyrophosphate transporter, ANK, in murine kidney cells.

BACKGROUND/AIMS: Mutation of the pyrophosphate transporter, ANK, results in progressive arthritis in mice. ANK is expressed in non-skeletal tissues including kidney. The aim was therefore to investigate ANK location at the cellular and subcellular level in renal cells. METHODS: RT-PCR identified a murine cell-line, mIMCD3, expressing ANK. The intra-renal distribution of ANK was determined by immunohistochemistry and the subcellular distribution in mIMCD3 cells by transfection of an ANK-NT-GFP fusion protein. Furthermore, an inactivating mutation of murine ank, Glu440X, and a gain of function mutation, Met48Thr, were tested to determine whether membrane traffic contributed to a transport defect. RESULTS: ANK is expressed in cells of the cortical collecting duct, as assessed by colocalisation with aquaporin 2 and at the lateral and apical plasma membranes of mIMCD-3 epithelial cells, as assessed by colocalisation with wheat germ agglutinin lectin (WGA). ANK-NT-GFP was also present in endoplasmic reticulum, Golgi, acidic endosomes and mitochondria. mIMCD3 expression of Glu440X ANK-NT-GFP shows evidence of Golgi retention whereas Met48Thr ANK-NT-GFP is unaltered at the plasma membrane compared to wild type. CONCLUSION: The intra-renal and subcellular localisation of ANK is consistent with pyrophosphate export from collecting duct cells and supports a role for ANK in limiting intra-renal calcium-crystal formation.     

The Myxoma Virus M-T5 Ankyrin Repeat Host Range Protein Is a Novel Adaptor That Coordinately Links the Cellular Signaling Pathways Mediated by Akt and Skp1 in Virus-Infected Cells

Most poxviruses express multiple proteins containing ankyrin (ANK) repeats accounting for a large superfamily of related but unique determinants of poxviral tropism. Recently, select members of this novel family of poxvirus proteins have drawn considerable attention for their potential roles in modulating intracellular signaling networks during viral infection. The rabbit-specific poxvirus, myxoma virus (MYXV), encodes four unique ANK repeat proteins, termed M-T5, M148, M149, and M150, all of which include a carboxy-terminal PRANC domain which closely resembles a cellular protein motif called the F-box domain. Here, we show that each MYXV-encoded ANK repeat protein, including M-T5, interacts directly with the Skp1 component of the host SCF ubiquitin ligase complex, and that the binding of M-T5 to cullin 1 is indirect via binding to Skp1 in the host SCF complex. To understand the significance of these virus-host protein interactions, the various binding domains of M-T5 were mapped. The N-terminal ANK repeats I and II were identified as being important for interaction with Akt, whereas the C-terminal PRANC/F-box-like domain was essential for binding to Skp1. We also report that M-T5 can bind Akt and the host SCF complex (via Skp1) simultaneously in MYXV-infected cells. Finally, we report that M-T5 specifically mediates the relocalization of Akt from the nucleus to the cytoplasm during infection with the wild-type MYXV, but not the M-T5 knockout version of the virus. These results indicate that ANK/PRANC proteins play a critical role in reprogramming disparate cellular signaling cascades to establish a new cellular environment more favorable for virus replication.Myxoma virus (MYXV) is a rabbit-specific poxvirus that has proven to be a useful model system to study the mechanism by which virus-encoded immunoregulatory proteins function to manipulate the various host immune responses during the course of viral infection (50). In its long-term evolutionary host (Sylvilagus sp.), MYXV causes a benign disease localized to the site of inoculation, but when the virus infects European rabbits (Oryctolagus cuniculus), it causes a rapid systemic and highly lethal infection called myxomatosis (13). The success of MYXV as a pathogen can be attributed to the ability of the virus to effectively avoid recognition and clearance by the immune systems of susceptible rabbit hosts. At the level of individual virus-infected cells, poxviruses, like MYXV, are particularly adept at binding and entering most mammalian cells, where they attempt to establish a favorable intracellular environment, which promotes viral replication. Thus, the ability of poxviruses to reconfigure or disable the various host antiviral responses of the infected cell directly dictates the outcome of a viral infection at the cellular level (28). To this end, poxviruses possess a large genomic capacity, and all encode a unique repertoire of immunoregulatory and host-interactive proteins that have evolved to specifically mediate a broad range of cellular processes critical for successful viral replication. To date, a large collection of poxvirus-encoded immunoregulatory proteins have been identified and characterized, including virokines, viroreceptors, signaling modulators, and inhibitors of various antiviral responses, such as apoptotic pathways and interferon signaling (43). More recently, a novel category of poxvirus ankyrin (ANK) repeat proteins have drawn considerable attention for their potential roles in modulating intracellular signaling networks during viral infection (48, 49, 53).With the exception of poxviruses, the ANK motif is not commonly reported in viruses, although numerous examples have been identified in eukaryotic, bacterial, and archaeal proteins (6). The ANK motif, a tandemly repeated consensus module of approximately 33 amino acid residues, has been demonstrated to mediate diverse protein-protein interactions between cellular proteins having a broad spectrum of functional roles (32, 42). Solved crystal structures have revealed a conserved fold structure of the ANK repeat unit, by which each repeat forms a characteristic helix-loop-helix structure with a beta-hairpin/loop region projecting out from the helices at a 90° angle (3, 16, 19, 26). However, the ANK fold appears to be defined by its structure rather than any conserved biological function since there is no specific conserved substrate or binding partner structure that is universally recognized by members of the superfamily.The majority of poxviral ANK repeat-containing proteins also include a conserved carboxy-terminal PRANC (pox protein repeats of ankyrin C terminus) motif, which closely resembles a cellular protein motif called the F-box domain (30). Characterized as substrate adaptors, F-box-containing host proteins function to recruit cellular substrate proteins to the SCF ubiquitin-ligase complex (named after their main components, Skp1, cullin 1 [CUL1], and an F-box protein), where the substrates selected by the complex are ubiquitinated and targeted for degradation by the proteasome (21, 45, 60). The process of selective ubiquitination is an essential regulatory step for many cellular processes, and the human genome encodes more than 70 different F-box proteins, which collectively are thought to specifically target a broad collection of cellular substrates for delivery to the SCF complex to initiate turnover (62).Accounting for the largest family of poxviral proteins, almost all chordopoxviruses encode multiple ANK repeat-containing proteins, some of which have been defined as viral host range or virulence factors (30). For example, canarypox virus encodes 51 ANK repeat proteins, accounting for greater than 20% of the genome; however, most other poxviruses express less than a half dozen ANK repeat proteins (52). MYXV encodes four unique ANK repeat proteins, termed M-T5, M148, M149, and M150, all of which have been described as virulence factors for myxomatosis in rabbits (5, 8, 33). The MYXV host range factor M-T5 was first characterized for its ability to regulate viral tropism within rabbit lymphocytes and, later, some classes of human cancer cell lines (33, 51). In human cancer cells, the direct physical interaction between M-T5 and the host cell Akt was shown to be a key restriction determinant for MYXV tropism in a subset referred to as type II cancer cells (56). Furthermore, M-T5 was shown to be functionally interchangeable with a host ANK repeat protein called PIKE-A, and the activation of Akt by either the viral M-T5 or the host PIKE-A protein was critical for MYXV permissiveness in type II human cancer cells (57). M-T5 was also demonstrated to protect MYXV-infected cells from virus-induced cell cycle arrest, a property which was linked to its ability to interact with a member of the host cell SCF complex called CUL1 (20). Unlike M-T5, no specific host binding partners or target substrates have yet been identified for M148, M149, or M150. However, in tumor necrosis factor alpha (TNF-α)-stimulated cells, M150 was shown to colocalize in the nucleus with NF-κB p65, suggesting that this MYXV protein may modulate the NF-κB pathway (8).In this study, we demonstrate that M-T5, M148, M149, and M150 all have functional carboxy-terminal PRANC/F-box-like domains and that each one can interact directly with the Skp1 component of the host SCF complex. We further examined the various binding domains of M-T5 and identified ANK repeats I and II as being important for interaction with Akt, whereas the PRANC/F-box-like domain was essential for binding to Skp1. We also show that the previously reported interaction of M-T5 with CUL1 was in fact, indirect linking of M-T5 to the host SCF complex via Skp1. More specifically, we investigated the ability of M-T5 to function as a molecular scaffold to link disparate cellular binding partners together within a single complex and report that the viral protein binds Akt and the SCF complex (via Skp1) simultaneously in MYXV-infected cells. Finally, we demonstrate that M-T5 specifically mediates the relocalization of Akt from the nucleus to the cytoplasm during MYXV infection. These results suggest that ANK/PRANC proteins, such as M-T5, play a critical role in reprogramming disparate cellular signaling cascades to establish a new cellular environment more favorable for viral replication.