Electrophoretic mobility of N- and C-terminal monoferric fragments of bovine transferrin phenotypes AA,D1D1, D2D2, and EE,and N-terminal amino acid sequences

Iron-saturated bovine transferrins A, D1, D2, and E were cleaved by trypsin yielding monoferric fragments. The N-terminal fragments (F) of transferrins A and D2 had identical mobility in cellulose acetate electrophoresis, that of transferrin D1 a slower mobility, and that of E a still slower mobility. The C-terminal fragments (S) gave multiple bands which were essentially identical in the case of transferrins A, D1, and E, but of slower mobility in the case of transferrin D2. All four variants had identical N-terminal amino acid sequences. The electrophoretic mobility of the C-terminal fragments was reduced by neuraminidase treatment, but the N-terminal fragments were unaffected. The four transferrin variants therefore appear to be made up from three electrophoretically distinguishable N-terminal halves and two C-terminal halves. The feature responsible for the electrophoretic double banding of homozygous bovine asialotransferrins is consistently associated with the C-terminal half of the molecule.     

Two newly identified sites in the N-terminal regulatory domain of Aurora-A are essential for auto-inhibition

Aurora-A, a centrosome-localized serine/threonine kinase, is over-expressed in multiple human cancers. We previously reported Zhang et al. (Biochem Biophys Res Commun 2007, 357:347–352) intramolecular inhibitory regulation of Aurora-A between its N-terminal (Nt) regulatory domain (amino acids 1–128, Nt) and C-terminal catalytic domain (aa 129–403, Cd). Here, we identified two essential sites located on the Nt of Aurora-A (Lys 99 and Lys 119) and demonstrate that mutation of either residue to Gly could cause the Nt and C-terminal lobes of the catalytic domain in Aurora-A to form a closed conformation, resulting in a loss of kinase activity. This inactive conformation was reversed by adding C26 peptide (274–299) or Ajuba, which is a required activator of Aurora-A. Over-expression of either mutant induced G2/M arrest. These results provide a basis for future anti-cancer studies targeting Aurora-A.     

Calmyrin1 binds to SCG10 protein (stathmin2) to modulate neurite outgrowth

Calmyrin1 (CaMy1) is an EF-hand Ca²⁺-binding protein expressed in several cell types, including brain neurons. Using a yeast two-hybrid screen of a human fetal brain cDNA library, we identified SCG10 protein (stathmin2) as a CaMy1 partner. SCG10 is a microtubule-destabilizing factor involved in neuronal growth during brain development. We found increased mRNA and protein levels of CaMy1 during neuronal development, which paralleled the changes in SCG10 levels. In developing primary rat hippocampal neurons in culture, CaMy1 and SCG10 colocalized in cell soma, neurites, and growth cones. Pull-down, coimmunoprecipitation, and proximity ligation assays demonstrated that the interaction between CaMy1 and SCG10 is direct and Ca²⁺-dependent in vivo and requires the C-terminal domain of CaMy1 (residues 99-192) and the N-terminal domain of SCG10 (residues 1-35). CaMy1 did not interact with stathmin1, a protein that is homologous with SCG10 but lacks the N-terminal domain characteristic of SCG10. CaMy1 interfered with SCG10 inhibitory activity in a microtubule polymerization assay. Moreover, CaMy1 overexpression inhibited SCG10-mediated neurite outgrowth in nerve growth factor (NGF)-stimulated PC12 cells. This CaMy1 activity did not occur when an N-terminally truncated SCG10 mutant unable to interact with CaMy1 was expressed. Altogether, these data suggest that CaMy1 via SCG10 couples Ca²⁺ signals with the dynamics of microtubules during neuronal outgrowth in the developing brain. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.     

Synthesis and evaluation of conformationally constrained peptide analogues as the Src SH3 domain binding ligands

Src kinase activity is regulated by the interaction of SH3 domain with protein sequences that are rich in proline residues. Identification of more potent SH3 domain binding ligands that can regulate Src kinase activity is a subject of major interest. Conformationally constrained peptides have been previously used for improving the binding potency of the Src SH2 domain binding peptide ligands and peptide substrates of the substrate-binding site of Src. A series of peptide analogues of Ac-VSLARRPLPPLP (1, Ac-VSL12, K_d = 0.34 μM) were synthesized by introducing conformational constraints to improve the binding affinity towards the Src SH3 domain. Peptides synthesized through cyclization between N-terminal to C-terminal [VSLARRPLPPLP] or N-terminal to side chain flanking residues (i.e., [^βAVS]LARRPLPPLP and [VSLE]RRPLPPLP) exhibited at least 6.4-fold less binding affinity (K_d = 2.19–4.85 μM) when compared to 1. The data suggest upon N-terminal cyclization with C-terminal or flanking residues, the interactions of the amino acids in the core RPLPPLP reduce significantly with the residues within the Src SH3 domain. Conformationally constrained peptide V[SLARRPLPPLP] (5) was synthesized through cyclization of C-terminal to the serine side chain and displayed a comparable binding affinity (K_d = 0.35 μM) towards the Src SH3 domain versus that of 1. Thus, this template may be used to optimize and generate more potent analogues with higher stability.     

Purification and N-terminal analyses of algal biliproteins

1. R-, B- and C-phycoerythrins and R- and C-phycocyanins were isolated and purified on a preparative scale by calcium phosphate chromatography, ammonium sulphate fractionation and crystallization. 2. The N-terminal residues of these biliproteins were analysed. Methionine is the only N-terminal residue of all the phycoerythrins, there being about 14 N-terminal residues per molecule of R- and B-phycoerythrins (mol.wt. 290000) and about 8 per molecule of C-phycoerythrin (mol.wt. 226000). Threonine (1 residue) is N-terminal in C-phycocyanin (mol.wt. 138000), and both threonine (about 1·3 residues) and methionine (5 residues) are N-terminal in R-phycocyanin (mol.wt. 273000). 3. Results suggest that the apoproteins of the various phycoerythrins are closely related, whereas C-phycocyanin has quite a different gross structure, and that R-phycocyanin contains two types of sub-unit, one related to C-phycocyanin and the other to the phycoerythrins.     

Effects of <Emphasis Type="Italic">N</Emphasis>- and <Emphasis Type="Italic">C</Emphasis>-terminal truncation of HP (2-20) from <Emphasis Type="Italic">Helicobacter pylori</Emphasis> ribosomal protein L1 (RPL1) on its anti-microbial activity

HP (2-20) [derived from the N-terminal region of Helicobacter pylori Ribosomal Protein L1 (RPL1)], a 19-mer peptide, possesses broad-spectrum anti-microbial activity. As the N- (residues 2–3) and C-terminal (residues 14–20) residues can be deleted without affecting antimicrobial activity, we have now determined the minimum chain length necessary for the retention of antimicrobial activity, and its mode of action. The N- (residues 2–3) and C-terminal (residues 17–20) truncated fragments [HP (4–16)] induce increased antibiotic activity against several bacterial strains without hemolysis. Flow cytometric analysis, scanning electron microscopy and fluorescence confocal microscopy revealed that HP (4–16) acted rapidly on the plasma membranes of the fungal cells in a salt- and energy-independent manner.Revisions requested 16 September 2004/1 November 2004; Revisions received 29 October 2004/8 December 2004     

Functional expression of Phanerochaete chrysosporium cellobiose dehydrogenase flavin domain in Escherichia coli

Cellobiose dehydrogenase (CDH; EC 1.1.99.18) is an extracellular glycosylated protein composed of two distinct domains, a C-terminal catalytic flavin domain and an N-terminal cytochrome-b-type heme domain, which transfers electrons from the flavin domain to external electron acceptors. The soluble flavin domain of the Phanerochaete chrysosporium CDH was successfully expressed in Escherichia coli. The enzyme showed dye-mediated CDH activity higher than that of the complete CDH, composed of flavin domain and heme domain, prepared using Pichia pastoris as the host microorganism. The ability to conveniently express the recombinant CDH flavin domain in E. coli provides great opportunities for the molecular engineering of the catalytic properties of CDH.     

Synthesis and antiproliferative activity of C- and N-terminal analogues of culicinin D

Culicinin D (1), a 10 amino acid peptaibol containing several unusual residues, has been shown to exhibit potent anticancer activity. Previous work in our group towards developing a structure-activity relationship (SAR) for this peptaibol has concentrated on replacement of the synthetically challenging AHMOD (3) and AMD (4) residues, resulting in the discovery of analogues with equivalent or better potency and simplified synthesis. The SAR of this peptaibol is extended in this work by investigating the effect of the N-terminal lipid tail and C-terminal amino alcohol, revealing the key contribution of each of these moieties on antiproliferative activity in a panel of breast and lung cancer cell lines.     

Domain-specific determinants of catalysis/substrate binding and the oligomerization status of barley UDP-glucose pyrophosphorylase

UDP-glucose (UDPG) pyrophosphorylase (UGPase) produces UDPG for sucrose and polysaccharide synthesis and glycosylation reactions. In this study, several barley UGPase mutants were produced, either single amino acid mutants or involving deletions of N- and C-terminal domains (Ncut and Ccut mutants, respectively) and of active site region (“NB loop”). The Del-NB mutant yielded no activity, whereas Ncut deletions and most of Ccut mutants, including short deletions at the so called “I-loop” region of C-terminal domain, as well as a single K260A mutant resulted in very low activity. For wt and the mutants, kinetics with UDPG were linear on reciprocal plots, whereas PPi at concentrations above 1 mM exerted strong substrate inhibition. Both K260A and most of the Ccut mutants had very high K_m with PPi (up to 33 mM), whereas Ncut deletions had greatly increased K_m with UDPG (up to 57 mM). Surprisingly, an 8 amino acid deletion from end of the C-terminus resulted in an enzyme (Ccut-8 mutant) with 44% higher activity when compared to wt, but with similar K_m values. Whereas Ccut-8 existed solely as a monomer, other deletion mutants had a more oligomerized status, e.g. Ncut mutants existing primarily as dimers. Overall, the data confirmed the essential role of NB loop in catalysis, but also pointed out to the role of both N- and C-termini for activity, substrate binding and oligomerization. The importance of oligomerization status for enzymatic activity of UGPase is discussed.     

Involvement of the <Emphasis Type="Italic">N</Emphasis>-terminal region and its characteristic coiled-coil fragment in the function and structure maintenance of <Emphasis Type="Italic">E. coli</Emphasis> LonA protease

The truncated form of E. coli LonA protease (EcLon) lacking the N-terminal fragment 1–172 (Lon173) and the variant with deleted coiled-coil (CC) fragment 173–283 (dCC-Lon, a deletion form) are produced and characterized to study the role of the N-terminal region in the functioning of this protease. A comparative analysis of the properties of full-length EcLon protease, dCC-Lon, and Lon173 as well as an earlier produced form with retained C-terminal region (235–280) of CC fragment, Lon235, is performed. As is shown, fragment 1–280 plays an important role in both formation of the ATPase site and maintenance of a stable EcLon protease conformation. Fragment 107–172 is of a paramount importance for implementation of the processive mechanism of ATP-dependent proteolysis.     

Functional expression and structural characterization of ORF cDNA encoding chitinase of the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae)

Chitin is an important component of the exoskeleton and peritrophic matrix in insects. Its bio-degradation is initiated by the endo-splitting chitinase. We cloned an ORF cDNA encoding chitinase from the last instar larva of the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), into E. coli to confirm its functionality. Its amino acid sequence was compared with previously described lepidopteran chitinases. S. exigua chitinase expression enhanced cell growth approx. 1.5 fold in transformed E. coli than in the wild strain in a 1% colloidal chitin-containing medium with insufficient regular nutrients. Compared with the wild strain, the two intracellular chitin degradation derivatives, glucosamine and N-acetylglucosamine, increased approx. 5.8 and 1.5 fold, respectively, and extracellular chitinase activity in the transformed strain was about 1.6 fold higher. The ORF of S. exigua chitinase-encoding cDNA including stop codon was composed of 1674 bp nucleotides and the calculated molecular weight of the deduced 557 amino acid residues was about 62.6 kDa. The ORF consisted of an N-terminal leading signal peptide (AA 1-20), a catalytic domain (AA 21-392), a linker region (AA 393-493), and a C-terminal chitin-binding domain (AA 494-557) showing a typical molting fluid chitinase structure. Phylogenetic analysis determined that all 5 noctuid chitinases were grouped together, while two bombycid enzymes and one tortricid enzyme mapped together in one lineage. In the noctuid group, the sub-lineages reflected their taxonomic relationships at the Genus level.     

Crystal structure of a nucleotide-binding domain of fatty acid kinase FakA from Thermus thermophilus HB8

Fatty acid kinase is necessary for the incorporation of exogenous fatty acids into membrane phospholipids. Fatty acid kinase consists of two components: a kinase component, FakA, that phosphorylates a fatty acid bound to a fatty acid-binding component, FakB. However, the molecular details underlying the phosphotransfer reaction remain to be resolved. We determined the crystal structure of the N-terminal domain of FakA bound to ADP from Thermus thermophilus HB8. The overall structure of this domain showed that the helical barrel fold is similar to the nucleotide-binding component of dihydroxyacetone kinase. The structure of the nucleotide-binding site revealed the roles of the conserved residues in recognition of ADP and Mg²⁺, but the N-terminal domain of FakA lacked the ADP-capping loop found in the dihydroxyacetone kinase component. Based on the structural similarity to the two subunits of dihydroxyacetone kinase complex, we constructed a model of the complex of T. thermophilus FakB and the N-terminal domain of FakA. In this model, the invariant Arg residue of FakB occupied a position that was spatially similar to that of the catalytically important Arg residue of dihydroxyacetone kinase, which predicted a composite active site in the Fatty acid kinase complex.     

Protein F: an adhesin of Streptococcus pyogenes binds fibronectin via two distinct domains

The binding of Streptococcus pyogenes to fibronectin (FN) enables the adherence of this pathogen to target epithelial cells, which is the first necessary step for initiation of infection. Binding is mediated by a bacterial surface protein termed protein F. Here we provide the complete structure of protein F and identify two domains responsible for binding to fibronectin. The first domain is located towards the C-terminal end of the molecule and is composed of five repeats of 37 amino acids that are completely repeated four times and a fifth time partially. The second domain is adjacent to the first domain and is located on the /V-terminal side of it. It is composed of a single stretch of 43 amino acids. Protein F expressed in Escherichia coli completely blocked the binding of fibronectin to S. pyogenes. However, mutant proteins that contained only one or the other of the two domains were only capable of partial blockage of binding. Complete blockage of binding of fibronectin could be achieved when a protein extract containing the N-terminal domain was mixed in a binding reaction with a protein extract containing the C-terminal domain. Similarly, a purified recombinant protein containing the two domains only, blocked the binding completely. In contrast, a purified recombinant protein containing just the C-terminal domain, blocked the binding partially. A clone exclusively expressing the C-terminal domain, completely blocked the binding of the 30 kDa N-terminal fragment of fibronectin to S. pyogenes, whereas a clone expressing the N-terminal domain failed to block the binding of this FN fragment. Thus, the two FN-binding domains of protein F are necessary for maximal bacterial binding and act in concert to enhance the binding to fibronectin. The possibility that the two domains bind to two different regions on the fibronectin molecule is discussed.     

Effect of N- and C-terminal deletions on the RNA N-glycosidase activity and the antigenicity of karasurin-A, a ribosome-inactivating protein from Trichosanthes kirilowii var. japonica

Karasurin-A, from root tubers of Trichosanthes kirilowii var. japonica, is a type I ribosome-inactivating protein (RIP) that displays activity of RNA N-glycosidase to remove an adenine in the conserved sarcin/ricin loop of the largest RNA in the ribosome. We expressed recombinant proteins of karasurin-A and its various mutants with N- or C-terminal deletions in Escherichia coli as fusion proteins with maltose-binding protein (MBP), and compared their enzymatic activities and antigenicities. Muteins of karasurin-A generated by deleting either the first 100 N-terminal or the last 30 C-terminal amino acid residues lost activity of RNA N-glycosidase. The mutant proteins whose 80 N-terminal or 20 C-terminal amino acids were deleted could depurinate rRNA although the activities were decreased drastically. The antigenicities of the recombinant proteins were considerably reduced by deleting 20 amino acid residues from either N- or C-terminal regions.Revisions requested 30 September 2004; Revisions received 22 October 2004     

Role of the C-terminal pro-domain of aqualysin I in the maturation and translocation of the precursor across the cytoplasmic membrane in Escherichia coli

Aqualysin I, which is a subtilisin-type, extracellular protease secreted by Thermus aquaticus YT-1, is synthesized as a unique precursor bearing pro-domains at both N- and C-terminus of the mature protease domain as well as an N-terminal signal peptide. To investigate the function of the C-terminal pro-domain in maturation and export pathway of the precursor in E. coli cells, aqualysin I variants were constructed in which deletion mutants of the C-terminal pro-domain lacking its own signal peptide were inserted into pIN-III-ompA3. When E. coli harboring wild type and mutant plasmids were induced by 0.2 mM IPTG, active aqualysin I was produced by heat treatment at 65 °C. Aqualysin I precursors with deletions of more than 5 amino acid residues at the C-terminal end of pro-domain were much more rapidly processed than that of wild type, indicating that the C-terminal pro-domain functions as a inhibitor for processing of aqualysin I precursor. With the wild type, most of aqualysin I was present in membrane fraction (probably the outer membrane), whereas for the truncated mutants, it remained in the cytoplasm, indicating that for deletion mutants, their precursors expressed in cells were not translocated across the cytoplasmic membrane, despite the existence of an N-terminal signal peptide.     

Characterization of lamprey fibrinopeptides

1. Lamprey fibrinopeptide B is a relatively large peptide made up of about 40 amino acid residues. The peptide is highly electronegative, containing a large number of aspartic acid residues and a tyrosine O-sulphate residue. 2. The amino acid sequence of the first 18 residues from the N-terminal end of fibrinopeptide B has been established. The C-terminal ends with the sequence Val-Arg. Fibrino-peptide B is released by both lamprey and bovine thrombins. 3. Lamprey fibrino-peptide A is a short peptide containing only eight residues. The proposed amino acid sequence is: Asp-Asp-Ser-Ile/Leu-Asp-Ser-Leu/Ile-ArgThis peptide is released by lamprey thrombin but not by bovine thrombin.     

Cell-surface-associated polypeptides CshA and CshB of high molecular mass are colonization determinants in the oral bacterium Streptococcus gordonii

The human oral bacterium Streptococcus gordonii expresses, on the cell surface, two antigenically related high-molecular-mass polypeptides denoted CshA and CshB, encoded by genes at separate chromosomal loci. The precursor form of CshA is composed of four distinct segments: (i) a 41-amino-acid residue leader peptide, (ii) W-terminal 42–878 residues, (iii) residues 879–2417 comprising 13 repeat blocks of 101 amino acid residues and three shorter blocks, and (iv) a C-terminal anchor domain similar to those present in some other Gram-positive bacterial cell-wall polypeptides. Insertional mutations within cshA reduced both cell-surface hydrophobicity and ability to adhere to oral Actinomyces naeslundii. Insertional mutations in cshB had less effect on hydrophobicity and coadherence. However, expression of both polypeptides was found to be necessary for streptococci to colonize the murine oral cavity.     

Subunit dissociation and stability alteration of <Emphasis Type="SmallCaps">d</Emphasis>-hydantoinase deleted at the terminal amino acid residue

Two variants of d-hydantoinase (HYD), created by deletion of one amino acid residue of at either the N- or C-terminus, were expressed in Escherichia coli and purified by two-step chromatography. Compared with HYD, HYDc1 with the C-terminal Arg deletion retained 43% activity, while HYDn1 with the N-terminal Ser deletion had no activity using dl-Hydantoin as substrate. Based on HYD dimer with a molecular weight of 103 kDa, HYDc1 is a monomer of 52 kDa and HYDn1 is a mixture of dimer and monomer. Moreover, HYDc1 displayed higher pH stability and lower thermal stability compared to HYD. In addition, the secondary and tertiary structures of HYDc1 were not significantly changed in contrast to the ones of HYDn1. All data imply that the C-terminal Arg of the HYD is crucial for homodimeric architecture of the enzyme, but non-essential for catalysis, while the N-terminal Ser is required for both conformation and catalysis of the enzyme.     

<Emphasis Type="Italic">In vitro</Emphasis> DNA-binding properties of a manganese response regulator (ManR) from <Emphasis Type="Italic">Anabaena</Emphasis> sp.

ManR of Anabaena sp. PCC 7120 is a manganese response regulator. Two ManR molecules bind to the specific DNA sequences at the same time, which was demonstrated by our previous results. From size exclusion chromatography, ManR exits as monomer in solution. Therefore, cooperative interactions of ManR–ManR play a role in DNA binding of the ManR, suggesting that ManR molecules bind co-operatively to DNA. When serial deletions of N-terminal of the ManR were also carried out the mutant proteins, ManRC111, ManRC130 and ManRC158, had completely lost the in DNA binding activity. Mutants ManRC 196, ManRC206, ManRC221 and ManRC230, however, could specifically bind to DNA, indicating that the amino acid residues between Val₁₆ and Ile₇₈ of the N-terminal of ManR are necessary for the DNA binding activity of C-terminal domain.Revisions requested 20 Ocotober 2004/15 November 2004; Revisions received 10 November/13 December 2004     

N-terminal amino acid sequence of C hordein

The C hordein (prolamin storage protein) fraction of barley endosperm has been purified and the N-terminal sequence of amino acids determined for 30 residues. No sequence was obtained for the B hordein fraction because the N-terminus was blocked.