Bacillus anthracis SlaQ Promotes S Layer Protein Assembly
ABSTRACT Bacillus anthracis vegetative forms assemble an S layer comprised of two S layer proteins, Sap and EA1. A hallmark of S layer proteins are their C terminal crystallization domains, which assemble into a crystalline lattice once these polypeptides are deposited on the bacterial surface via association between their N terminal S layer homology domains and the secondary cell wall polysaccharide. Here we show that slaQ, encoding a small cytoplasmic protein conserved among pathogenic bacilli elaborating S layers, is required for the efficient secretion and assembly of Sap and EA1. S layer protein precursors cosediment with SlaQ, and SlaQ appears to facilitate Sap assembly. Purified SlaQ polymerizes and when mixed with purified Sap promotes the in vitro formation of tubular S layer structures. A model is discussed whereby SlaQ, in conjunction with S layer secretion factors SecA2 and SlaP, promotes localized secretion and S layer assembly in B. anthracis. IMPORTANCE S layer proteins are endowed with the propensity for self assembly into crystalline arrays. Factors promoting S layer protein assembly have heretofore not been reported. We identified Bacillus anthracis SlaQ, a small cytoplasmic protein that facilitates S layer protein assembly in vivo and in vitro.
Journal of bacteriology