Sortases and pilin elements involved in pilus assembly of Corynebacterium diphtheriae
Sortases and pilin elements involved in pilus assembly of Corynebacterium diphtheriae
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DOI：
10.1111/j.1365-2958.2004.04117.x
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发表时间：
2004-07-01
影响因子：
3.6
通讯作者：
Schneewind, O
中科院分区：
文献类型：
--
作者：
Hung, TT;Marraffini, LA;Schneewind, O
白喉棒状杆菌SpaA菌毛由SpaA、SpaB和SpaC三个菌毛亚基组成。主要的毛蛋白SpaA沿毛轴均匀分布，而SpaB则有规律的间隔，SpaC似乎位于毛尖。白喉菌丝的组装需要pilin基序和SpaA的c端分选信号，并提出了一种有序交联机制，即pilin特异性分选酶在分选信号处切割前体蛋白，并涉及pilin基序的侧链氨基，从而在pilin亚基之间产生共价键。我们在这里展示了SpaA毛蛋白前体的两个元素，毛蛋白基序和分选信号，在一起就足以通过一个需要分选酶a基因（srtA）功能的过程来促进另一种分泌蛋白的聚合。另外五个分选酶基因对于SpaA菌毛的组装是必不可少的。此外，SpaB整合到SpaA菌毛中需要SpaA E盒基序内的谷氨酸残基，这一特征在其他革兰氏阳性病原体中被发现是保守的，这些革兰氏阳性病原体编码具有分选信号和匹林基序的分选酶和匹林亚基基因。当naeslundii型放线菌的主要毛状亚基FimA在棒状菌中表达时，白喉C. NCTC13129菌株将FimA聚合形成短纤维。尽管白喉链球菌不依赖于其他放线菌基因进行FimA聚合，但这一过程涉及到pilin基序和FimA的分选信号以及线状细菌分选酶D （SrtD）。因此，革兰氏阳性菌的菌毛组装似乎是通过前体蛋白有序交联的普遍机制发生的，其多种保守特征被指定的分选酶识别。
Corynebacterium diphtheriae SpaA pili are composed of three pilin subunits, SpaA, SpaB and SpaC. SpaA, the major pilin protein, is distributed uniformly along the pilus shaft, whereas SpaB is observed at regular intervals, and SpaC seems to be positioned at the pilus tip. Pilus assembly in C. diphtheriae requires the pilin motif and the C-terminal sorting signal of SpaA, and is proposed to occur by a mechanism of ordered cross-linking, whereby pilin-specific sortase enzymes cleave precursor proteins at sorting signals and involve the side-chain amino groups of pilin motif sequences to generate covalent linkages between pilin subunits. We show here that two elements of SpaA pilin precursor, the pilin motif and the sorting signal, are together sufficient to promote the polymerization of an otherwise secreted protein by a process requiring the function of the sortase A gene (srtA). Five other sortase genes are dispensable for SpaA pilus assembly. Further, the incorporation of SpaB into SpaA pili requires a glutamic acid residue within the E box motif of SpaA, a feature that is found to be conserved in other Gram-positive pathogens that encode sortase and pilin subunit genes with sorting signals and pilin motifs. When the main fimbrial subunit of Actinomyces naeslundii type I fimbriae, FimA, is expressed in corynebacteria, C. diphtheriae strain NCTC13129 polymerized FimA to form short fibres. Although C. diphtheriae does not depend on other actinomycetal genes for FimA polymerization, this process involves the pilin motif and the sorting signal of FimA as well as corynebacterial sortase D (SrtD). Thus, pilus assembly in Gram-positive bacteria seems to occur by a universal mechanism of ordered cross-linking of precursor proteins, the multiple conserved features of which are recognized by designated sortase enzymes.