Antigen 43 (Ag43) is an abundant outer membrane protein in Escherichia coli belonging to the autotransporter family. Structure-function relationships of Ag43 proposed on the basis of experimental work and in silico analysis are discussed in context of insights derived from molecular modeling. New sequence analysis sheds light on the phylogeny of the allelic variants of the Ag43-encoding gene and identifies two distinct families that appear to be distributed between specific pathogenic and commensal isolates. The molecular mechanism that controls expression by phase variation to create population heterogeneity is discussed. Proposed roles of Ag43 expression for E. coli are summarized and the studies are put into perspective regarding the role of allelic variants, genetic background of the bacterial strain, and control of expression by phase variation. We conclude that future studies need to take into account these variables to obtain a complete understanding of the contribution of Ag43 expression to E. coli biology.

中文翻译：

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Ag43（流感）的调节和功能。

抗原 43 (Ag43) 是大肠杆菌中丰富的外膜蛋白，属于自转运蛋白家族。基于实验工作和计算机分析提出的 Ag43 的结构 - 功能关系在从分子建模得出的见解的背景下进行了讨论。新的序列分析揭示了 Ag43 编码基因的等位基因变异的系统发育，并确定了两个不同的家族，它们似乎分布在特定的致病性和共生分离株之间。讨论了通过相位变化控制表达以产生种群异质性的分子机制。总结了 Ag43 表达对大肠杆菌的拟议作用，并对等位基因变异的作用、细菌菌株的遗传背景、和通过相位变化控制表达。我们得出结论，未来的研究需要考虑这些变量，以全面了解 Ag43 表达对大肠杆菌生物学的贡献。