Extracytoplasmic function

Cao M, Moore CM, Helmann JD. 2005. Bacillus subtilis paraquat resistance is directed by Om, an extracytoplasmic function sigma factor, and is conferred by YqjL and BcrC. J Bacterial 187(9) 2948-2956. 

Turning disorder to order can hold functionality SecA is a helicase-like motor coupling ATP hydrolysis with the translocation of extracytoplasmic substrates.119 It was shown that SecA takes advantages of such a mechanism, namely... 

The purpose of this review is to discuss what is currently known about the different functions of metalloprotease-disintegrins, and to highlight some of the most interesting and pressing questions that have now been raised about this intriguing protein family. A brief summary of the known properties of snake venom disin-tegrins and metalloproteases is followed by a discussion of the role of membrane-anchored metalloprotease-disintegrins in cell-cell interactions and proteolysis of extracytoplasmic or extracellular protein domains. 

There are also three isoforms of the B subunit 61, 62, and B3. Presumably, each isoform is expressed along with its a partner and assembled in the endoplasnric reticulum as an a-6 heterodimer. The B subunit has a single transmembrane segment and is a type II membrane protein, with the N-terminal cytoplasmic and the C-terminal sequence extracytoplasmic. There are three N-linked glycosylation consensus sequences (NXT or NXS) and three disulfide bonds in the extracytoplasmic domain of the B subunit. The function of the 6 subunit of this ATPase is not very clear. Alteration of its structure by disulfide reduction inhibits ATPase activity. In its absence, the a subunit is unstable and does not reach the plasma membrane, so it is required for structural stability. Why the a subunit is unstable in the absence of the B subunit is not obvious, because the plasma membrane Ca ATPase has similar topology but does not require a B subunit for stable plasma membrane expression. It seems that membrane insertion of the M5 and subsequent domains depends on expression of the B subunit. Only the K countertransport pumps require a B subunit, and modification of this protein modifies pump kinetics. 

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