Behavioural and chemical mechanisms behind a Mediterranean ant–ant association

1. Interspecific competition among ants is common, and so is competitive exclusion among dominant ant species. In contrast, specific associations between non‐parasitic ant species are rare, especially in the temperate zones. As an exception, the subordinate ant Camponotus lateralis frequently co‐occurs with the dominant Crematogaster scutellaris but rarely with other dominant ants. 2. This association is one of various associations between Camponotus and Crematogaster species across the world. However, the mechanisms behind these co‐occurences are largely unknown. 3. In the present study, we therefore investigated the association of Ca. lateralis and Cr. scutellaris. We studied the spatial association of the nests, interspecific aggression, both species' cuticular hydrocarbon profiles, and their propensity to follow the other species' pheromone trails. 4. Crematogaster scutellaris usually attacked and displaced the generally submissive Ca. lateralis, but was significantly less aggressive at jointly used trails. Camponotus nests were always in close proximity to Crematogaster nests. 5. The cuticular hydrocarbons of both species consisted of alkanes with chain lengths between C21 and C35. The two species had 25 hydrocarbons in common, including mono‐, di‐, and tetramethyl alkanes. Despite this qualitative similarity, however, the quantitative hydrocarbon composition differed between the two species. 6. Camponotus lateralis followed artificial trails containing trail pheromones of Cr. scutellaris, but the latter did not follow Ca. lateralis trail pheromones. Interspecific trail‐following by Camponotus, but not vice versa, has been observed in another Camponotus–Crematogaster association and may be a more general mechanism that facilitates associations between the two ant genera.     

Inhibition of NF-kappaB activity by IkappaBbeta in association with kappaB-Ras

IkappaBbeta, one of the major IkappaB proteins, is only partially degraded in response to most extracellular signals. However, the molecular mechanism of this event is unknown. We show here that IkappaBbeta exists in at least two different forms: one that is bound to the NF-kappaB dimer and the other bound to both NF-kappaB and kappaB-Ras, a Ras-like small G protein. Removal of cellular kappaB-Ras enhances whereas excess kappaB-Ras blocks induced IkappaBbeta degradation. Remarkably, kappaB-Ras functions in both GDP- and GTP-bound states, and mutations of the conserved guanine-binding residues of kappaB-Ras abrogate its ability to block degradation of IkappaBbeta. kappaB-Ras also directly blocks the in vitro phosphorylation of IkappaBbeta by IKKbeta. These observations suggest that IkappaBbeta in the ternary complex is resistant to degradation by most signals. We suggest that specific signals, in addition to those that activate only IKK, are essential for the complete degradation of IkappaBbeta.     

The ATP/metallothionein interaction: NMR and STM

We have previously established that ATP binds to mammalian metallothionein-2 (MT). The interaction between ATP and MT and the associated conformational change of the protein affect the sulfhydryl reactivity and zinc transfer potential of MT [Jiang, L.-J., Maret, W., and Vallee, B. L. (1998) The ATP-metallothionein complex. Proc. Natl. Acad. Sci. U.S.A. 95, 9146-9149]. NMR spectroscopic investigations have now provided further evidence for the interaction. (35)Cl NMR spectroscopy has further identified chloride as an additional biological MT ligand, which can interfere with the interaction of ATP with MT. (1)H NMR/TOCSY spectra demonstrate that ATP binding affects the N- and C-terminal amino acids of the MT molecule. Scanning tunneling microscopy recorded images of single MT molecules in buffered solutions. Moreover, this technique demonstrates that the otherwise nearly linear MT molecule bends by about 20 degrees at its central hinge region between the domains in the presence of ATP. These results may bear on the development of mild obesity in MT null mice and the role of MT in the regulation of energy balance. The interaction suggests a mechanism for the cellular translocation, retention, and reactivity of the ATP*MT complex in the mitochondrial intermembrane space. Both MT and ATP are localized there, and MT and thionein alternately bind and release zinc, thereby affecting mitochondrial respiration.     

A role for the lissencephaly gene LIS1 in mitosis and cytoplasmic dynein function

Mutations in the LIS1 gene cause gross histological disorganization of the developing human brain, resulting in a brain surface that is almost smooth. Here we show that LIS1 protein co-immunoprecipitates with cytoplasmic dynein and dynactin, and localizes to the cell cortex and to mitotic kinetochores, which are known sites for binding of cytoplasmic dynein. Overexpression of LIS1 in cultured mammalian cells interferes with mitotic progression and leads to spindle misorientation. Injection of anti-LIS1 antibody interferes with attachment of chromosomes to the metaphase plate, and leads to chromosome loss. We conclude that LIS1 participates in a subset of dynein functions, and may regulate the division of neuronal progenitor cells in the developing brain.     

Light intermediate chain 1 defines a functional subfraction of cytoplasmic dynein which binds to pericentrin

The light intermediate chains (LICs) of cytoplasmic dynein consist of multiple isoforms, which undergo post-translational modification to produce a large number of species separable by two-dimensional electrophoresis and which we have proposed to represent at least two gene products. Recently, we demonstrated the first known function for the LICs: binding to the centrosomal protein, pericentrin, which represents a novel, non-dynactin-based cargo-binding mechanism. Here we report the cloning of rat LIC1, which is approximately 75% homologous to rat LIC2 and also contains a P-loop consensus sequence. We compared LIC1 and LIC2 for the ability to interact with pericentrin, and found that only LIC1 will bind. A functional P-loop sequence is not required for this interaction. We have mapped the interaction to the central region of both LIC1 and pericentrin. Using recombinant LICs, we found that they form homooligomers, but not heterooligomers, and exhibit mutually exclusive binding to the heavy chain. Additionally, overexpressed pericentrin is seen to interact with endogenous LIC1 exclusively. Together these results demonstrate the existence of two subclasses of cytoplasmic dynein: LIC1-containing dynein, and LIC2-containing dynein, only the former of which is involved in pericentrin association with dynein.     

High-resolution imaging reveals indirect coordination of opposite motors and a role for LIS1 in high-load axonal transport

The specific physiological roles of dynein regulatory factors remain poorly understood as a result of their functional complexity and the interdependence of dynein and kinesin motor activities. We used a novel approach to overcome these challenges, combining acute in vivo inhibition with automated high temporal and spatial resolution particle tracking. Acute dynein inhibition in nonneuronal cells caused an immediate dispersal of diverse forms of cargo, resulting from a sharp decrease in microtubule minus-end run length followed by a gradual decrease in plus-end runs. Acute LIS1 inhibition or LIS1 RNA interference had little effect on lysosomes/late endosomes but severely inhibited axonal transport of large, but not small, vesicular structures. Our acute inhibition results argue against direct mechanical activation of opposite-directed motors and offer a novel approach of potential broad utility in the study of motor protein function in vivo. Our data also reveal a specific but cell type-restricted role for LIS1 in large vesicular transport and provide the first quantitative support for a general role for LIS1 in high-load dynein functions.     

Computer-graphics interpretations of residue exchanges between the alpha, beta and gamma subunits of human-liver alcohol dehydrogenase class I isozymes

Three-dimensional models of human alcohol dehydrogenase subunits have been constructed, based on the homologous horse enzyme, with computer graphics. All types of class I subunits (alpha, beta, and gamma) and the major allelic variants (beta 1/beta 2 and gamma 1/gamma 2) have been studied. Residue differences between the E-type subunit of the horse enzyme and any of the subunits of the human isozymes occur at 64 positions, about half of which are isozyme-specific. About two thirds of the substitutions are at the surface and all differences can be accommodated in highly conserved three-dimensional structures. The model of the gamma isozyme is most similar to the crystallographically analyzed horse liver E-type alcohol dehydrogenase, and has all the functional residues identical to those of the E subunit except for one which is slightly smaller: Val-141 in the substrate pocket. The residues involved in coenzyme binding are generally conserved between the horse enzyme and the alpha, beta, and gamma types of the human enzyme. In contrast, single exchanges of these residues are the ones involved in the major allelic differences (beta 1 versus beta 2 and gamma 1 versus gamma 2), which affects the overall rate of alcohol oxidation since NADH dissociation is the rate-determining step. Residue 47 is His in beta 2 and Arg in the beta 1, gamma 1, and gamma 2 subunits, and in horse liver alcohol dehydrogenase. Both His and Arg can make a hydrogen bond to a phosphate oxygen atom of NAD; hence the lower turnover rate of beta 1 apparently derives from a charge effect. The substitution to Gly in the alpha subunit results in one less hydrogen bond in NAD binding, and consequently in rapid dissociation. This may explain why the overall rate is an order of magnitude faster than that of beta 1. The important difference between gamma 1 and gamma 2 is an exchange at position 271 from Arg to Gln which can give a hydrogen bond from Gln in gamma 2 to the adenine of NAD. The tighter binding to gamma 2 can account for the slower overall catalytic rate in this isozyme. The kinetics and interactions of cyclohexanol and benzyl alcohol with the isozymes were judged by docking experiments using an interactive fitting program.(ABSTRACT TRUNCATED AT 400 WORDS)     

A Nup133-dependent NPC-anchored network tethers centrosomes to the nuclear envelope in prophase

Maintenance of stable E-cadherin-dependent adhesion is essential for epithelial function. The small GTPase Rac is activated by initial cadherin clustering, but the precise mechanisms underlying Rac-dependent junction stabilization are not well understood. Ajuba, a LIM domain protein, colocalizes with cadherins, yet Ajuba function at junctions is unknown. We show that, in Ajuba-depleted cells, Rac activation and actin accumulation at cadherin receptors was impaired, and junctions did not sustain mechanical stress. The Rac effector PAK1 was also transiently activated upon cell-cell adhesion and directly phosphorylated Ajuba (Thr172). Interestingly, similar to Ajuba depletion, blocking PAK1 activation perturbed junction maintenance and actin recruitment. Expression of phosphomimetic Ajuba rescued the effects of PAK1 inhibition. Ajuba bound directly to Rac·GDP or Rac·GTP, but phosphorylated Ajuba interacted preferentially with active Rac. Rather than facilitating Rac recruitment to junctions, Ajuba modulated Rac dynamics at contacts depending on its phosphorylation status. Thus, a Rac-PAK1-Ajuba feedback loop integrates spatiotemporal signaling with actin remodeling at cell-cell contacts and stabilizes preassembled cadherin complexes.     

PKA-dependent dynein switching from lysosomes to adenovirus: A novel form of host–virus competition

Cytoplasmic dynein is responsible for transport of several viruses to the nucleus. Adenovirus recruits dynein directly. Transport depends on virus-induced activation of protein kinase A (PKA) and other cellular protein kinases, whose roles in infection are poorly understood. We find that PKA phosphorylates cytoplasmic dynein at a novel site in light intermediate chain 1 (LIC1) that is essential for dynein binding to the hexon capsid subunit and for virus motility. Surprisingly, the same LIC1 modification induces a slow, but specific, dispersal of lysosomes (lyso)/late endosomes (LEs) that is mediated by inhibition of a newly identified LIC1 interaction with the RILP (Rab7-interacting lysosomal protein). These results identify an organelle-specific dynein regulatory modification that adenovirus uses for its own transport. PKA-mediated LIC1 phosphorylation causes only partial lyso/LE dispersal, suggesting a role for additional, parallel mechanisms for dynein recruitment to lyso/LEs. This arrangement provides a novel means to fine tune transport of these organelles in response to infection as well as to developmental and physiological cues.