The Oca family is a novel class of autotransporter-adhesins with highest structural similarity in their C-terminal transmembrane region, which supposedly builds a beta-barrel pore in the outer membrane (OM). The prototype of the Oca family is YadA, an adhesin of Yersinia enterocolitica and Yersinia pseudotuberculosis. Protein secretion in gram-negative bacteria is faced with the serious problem of traversing two different membrane-lipid bilayers. Therefore, several secretory pathways have evolved, which were classified into five different types (9,11,20,29,51). Recently, even two novel multicomponent secretion systems, type VI and type VII secretion, were introduced (1,31,40). While all other types engage a whole machinery of protein exporting helper proteins, the type V secretion mechanism is thought to be less complex, since all necessary information for transport through both membranes is contained in the secreted protein itself, which has also led to the term "autotransporter" protein (20). With over 700 identified proteins to date, the type V secretion family is the largest group, and many of its members are also confirmed virulence factors with effector functions such as adherence, invasion, proteolysis, cytotoxicity, serum resistance, and cell-to-cell spread (14,37). An N-terminal signal peptide is Sec dependently cleaved during passage through the inner membrane, while the process of translocation through the outer membrane (OM) is still unresolved. The C-terminal region forms a beta-barrel pore before or during integration into the OM and is essential for translocation of the N-terminal passenger domain across the OM (20). However, the detailed process of passenger domain translocation remains unclear (6). Different models have been proposed to approach this issue. According to the hairpin and the threading model, the beta-barrel primarily integrates into the OM, and the passenger domain slides through the pore starting with the C or N terminus (21,36,39). The multimeric model suggests that the passenger domain is translocated to the bacterial surface through a central channel built by a multimeric complex of beta-barrel pores (52), while the Omp85 model involves the OM protein Omp85/YaeT in the translocation process (54, 55).Previously, we could demonstrate that the Yersinia adhesin YadA of Yersinia enterocolitica and Yersinia pseudotuberculosis is the prototype of a novel class of oligomeric autotransporter adhesins (42), which we termed Oca (for oligomeric coiled-coil adhesins), which can be found in alpha-, beta-, and gammaproteobacteria. In addition to YadA, several other family members, such as Hia and Hsf of Haemophilus influenzae, UspA1 and UspA2 of Moraxella catarrhalis, Eib proteins of Escherichia coli, or NadA of Neisseria meningitidis, have been identified in the last few years (8,12,15,23,45,48). Conventional autotransporters are monomeric proteins and form their C-terminal translocator domain (TLD) with 12 transmem-

Exposure to arsenic compounds may lead to skin and lung cancer and various disorders such as vascular disease and peripheral neuropathy in humans. Peripheral arsenic neurotoxicity has been demonstrated clinically and in electrophysiological studies. Patients intoxicated with arsenic show neurological symptoms in their feet and hands. These patients show significantly lower nerve conduction velocities (NCVs) in their peripheral nerves in comparison with controls. The mechanism of arsenic peripheral nervous system (PNS) toxicity, however, has never been described before. This is the first study to investigate the toxicity of arsenic on the PNS. Male Wistar rats were exposed to arsenite given as a single dose i.v. After sacrifice, sciatic nerves were excised and the protein composition was analysed. Protein analysis of sciatic nerves showed disappearance of neurofilament and fibroblast proteins in rats treated with arsenite doses of 15 and 20 mg/kg in comparison with the control groups. Some fibroblast protein bands had disappeared in the 20-mg/kg dose group. The analysed neurofilament-M and-L proteins decreased dose dependency over time. arsenic affects the composition of proteins in the rat sciatic nerve, especially the neurofilaments. The reduction of signals in Western blot analysis reveals changes in cytoskeletal composition, which may well lead to neurotoxic effects in vivo.

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