鼠伤寒沙门氏菌的maltoporin:序列和折叠模型。
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Francoz E, Molla Dassa E,停下来W, Hofnung M
鼠伤寒沙门氏菌的maltoporin:序列和折叠模型。
Res Microbiol。1990年11 - 12月,141 (9):1039 - 59。
- PubMed ID
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2092357 (在PubMed]
- 文摘
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羊鼠伤寒沙门氏菌基因的序列测定。它编码从美国培养的羔羊的前体蛋白(pre-LamBS.t。452年残留),提供了广泛的同源性与pre-LamB蛋白质从大肠杆菌(pre-LamBE.c。446残基)。pre-LamBS.t的前三分之一。是最保守的,4%的变化和严格的身份之间的信号肽。最后是否包含五个“变量”段超过50%的残留在哪里改变了对LamBE.c . .一分之三变量段8到14长残留,只包含替换,而两个远的是24和29残留长,还包括插入和删除。值得注意的是,变量部分基本上对应区域预测extramembranous循环在我们的2 d LamBE.c折叠模型。他们用守恒的预测transmembranous段备用。 Four of the variable regions were predicted to be cell-surface-exposed loops on the basis of genetic and immunological data, while one of them (region II) was predicted to be periplasmic on the sole basis of folding rules. The LamB protein from S. typhimurium can substitute for the LamB protein from E. coli for maltodextrins binding and transport, but not for infection by any of the known E. coli phages using LamBE.c. for adsorption. A tetrapeptide, RGDS, assumed to be responsible for mammalian cell aggregation by LamBE.c. is conserved in LamBS.t., suggesting that it could have a functional role. The conservation of the binding and transport activity can be accounted for by the conservation of the regions known to be directly involved, namely the first third of the protein and a region corresponding to 352 to 374 of LamBS.t.. The phage resistance can be attributed to the variability of the four cell-surface-exposed loops previously identified as essential for phage adsorption. These results, together with those obtained with polyclonal and monoclonal antibodies directed against known LamB regions, strongly support the folding model presented for LamBE.c. and the idea that it can essentially be extended to LamBS.t., except perhaps for a region between residues 155 and 245. We propose that the existence of variable regions is due essentially, and perhaps only, to the local lack of structural constraints in the protein. The intergenic region between lamB and the following gene, malM, comprises conserved segments, including one palindromic unit.