College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
Acta Crystallogr D Struct Biol. 2021 Aug 1;77(Pt 8):1040-1049. doi: 10.1107/S2059798321006768. Epub 2021 Jul 27.
The β-link is a composite protein motif consisting of a G1β β-bulge and a type II β-turn, and is generally found at the end of two adjacent strands of antiparallel β-sheet. The 1,2-positions of the β-bulge are also the 3,4-positions of the β-turn, with the result that the N-terminal portion of the polypeptide chain is orientated at right angles to the β-sheet. Here, it is reported that the β-link is frequently found in certain protein folds of the SCOPe structural classification at specific locations where it connects a β-sheet to another area of a protein. It is found at locations where it connects one β-sheet to another in the β-sandwich and related structures, and in small (four-, five- or six-stranded) β-barrels, where it connects two β-strands through the polypeptide chain that crosses an open end of the barrel. It is not found in larger (eight-stranded or more) β-barrels that are straightforward β-meanders. In some cases it initiates a connection between a single β-sheet and an α-helix. The β-link also provides a framework for catalysis in serine proteases, where the catalytic serine is part of a conserved β-link, and in cysteine proteases, including M of human SARS-CoV-2, in which two residues of the active site are located in a conserved β-link.
β-连接是一种由 G1ββ-突环和 II 型β-转角组成的复合蛋白结构基序，通常位于两条反平行β-折叠的末端。β-突环的 1,2 位也是β-转角的 3,4 位，因此多肽链的 N 端部分垂直于β-片层。本文报道称，β-连接在 SCOPe 结构分类的某些特定蛋白质折叠中经常出现，连接β-片层和蛋白质的另一个区域。它出现在β-三明治和相关结构中连接一个β-片层到另一个β-片层的位置，以及在小（四、五或六股）β-桶中连接两条β-链的位置，其中通过穿过桶开口端的多肽链连接。它不存在于更大（八股或更多）的直 β-弯管中。在某些情况下，它会启动单个β-片层和α-螺旋之间的连接。β-连接还为丝氨酸蛋白酶中的催化提供了一个框架，其中催化丝氨酸是保守β-连接的一部分，在半胱氨酸蛋白酶中也是如此，包括人 SARS-CoV-2 的 M 蛋白，其中活性位点的两个残基位于保守的β-连接中。
