Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America.
PLoS One. 2010 Dec 30;5(12):e15888. doi: 10.1371/journal.pone.0015888.
The Haemophilus influenzae HMW1 adhesin is an important virulence exoprotein that is secreted via the two-partner secretion pathway and is glycosylated at multiple asparagine residues in consensus N-linked sequons. Unlike the heavily branched glycans found in eukaryotic N-linked glycoproteins, the modifying glycan structures in HMW1 are mono-hexoses or di-hexoses. Recent work demonstrated that the H. influenzae HMW1C protein is the glycosyltransferase responsible for transferring glucose and galactose to the acceptor sites of HMW1. An Actinobacillus pleuropneumoniae protein designated ApHMW1C shares high-level homology with HMW1C and has been assigned to the GT41 family, which otherwise contains only O-glycosyltransferases. In this study, we demonstrated that ApHMW1C has N-glycosyltransferase activity and is able to transfer glucose and galactose to known asparagine sites in HMW1. In addition, we found that ApHMW1C is able to complement a deficiency of HMW1C and mediate HMW1 glycosylation and adhesive activity in whole bacteria. Initial structure-function studies suggested that ApHMW1C consists of two domains, including a 15-kDa N-terminal domain and a 55-kDa C-terminal domain harboring glycosyltransferase activity. These findings suggest a new subfamily of HMW1C-like glycosyltransferases distinct from other GT41 family O-glycosyltransferases.
流感嗜血杆菌 HMW1 黏附素是一种重要的毒力外蛋白，通过双伙伴分泌途径分泌，并在多个天冬酰胺残基上发生糖基化，这些残基符合 N 连接糖基化序列。与真核 N 连接糖蛋白中发现的高度分支聚糖不同，HMW1 中的修饰聚糖结构为单己糖或二己糖。最近的工作表明，流感嗜血杆菌 HMW1C 蛋白是负责将葡萄糖和半乳糖转移到 HMW1 受体部位的糖基转移酶。一种被指定为 ApHMW1C 的胸膜肺炎放线杆菌蛋白与 HMW1C 具有高度同源性，并被分配到 GT41 家族，该家族仅包含 O-糖基转移酶。在这项研究中，我们证明了 ApHMW1C 具有 N-糖基转移酶活性，能够将葡萄糖和半乳糖转移到 HMW1 中的已知天冬酰胺部位。此外，我们发现 ApHMW1C 能够弥补 HMW1C 的缺乏，并在整个细菌中介导 HMW1 的糖基化和黏附活性。初步的结构功能研究表明，ApHMW1C 由两个结构域组成，包括 15kDa 的 N 端结构域和具有糖基转移酶活性的 55kDa C 端结构域。这些发现表明了 HMW1C 样糖基转移酶的一个新亚家族，与其他 GT41 家族的 O-糖基转移酶不同。
