Garduño R A, Phipps B M, Baumeister W, Kay W W
Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
J Struct Biol. 1992 Nov-Dec;109(3):184-95. doi: 10.1016/1047-8477(92)90030-e.
The fish pathogen Aeromonas salmonicida possesses a regular surface layer (or A-layer) which is an important virulence determinant. The A-protein, a single bilobed protein organized in a p4 lattice of M4C4 arrangement with two morphological domains, comprises this layer. The role of divalent cations in the A-layer structure was studied to better understand A-protein subunit interactions affecting structural flexibility and function. Divalent cation bridges were found to be involved in the integrity of the A-layer. Two novel A-layer patterns were formed as the result of growth under calcium limitation or by chelation of divalent cations with EDTA or EGTA, thereby constituting the first reported case of formation of distinct regular arrays upon divalent cation depletion. Furthermore, under these conditions A-protein was sometimes released as tetrameric units, rather than in monomeric form. The formation of the two novel patterns is best explained by a sequence of structural rearrangements, following disruption of only one of the two A-layer morphological units, that is, those held together by divalent cation bridges. The free tetrameric units represent four A-protein subunits clustered around the unaffected four-fold axis.
鱼类病原菌杀鲑气单胞菌具有规则的表面层（或A层），这是一个重要的毒力决定因素。A蛋白是一种单叶双蛋白，以M4C4排列的p4晶格形式组织，有两个形态结构域，构成了这一层。研究了二价阳离子在A层结构中的作用，以更好地理解影响结构灵活性和功能的A蛋白亚基相互作用。发现二价阳离子桥参与A层的完整性。在钙限制条件下生长或用乙二胺四乙酸（EDTA）或乙二醇双四乙酸（EGTA）螯合二价阳离子后，形成了两种新的A层模式，这是首次报道的二价阳离子耗尽时形成不同规则阵列的情况。此外，在这些条件下，A蛋白有时以四聚体形式释放，而不是单体形式。两种新模式的形成最好用结构重排序列来解释，这种重排仅发生在两个A层形态结构单元中的一个被破坏之后，即那些由二价阳离子桥连接在一起的单元。游离的四聚体单元代表围绕未受影响的四重轴聚集的四个A蛋白亚基。
