Loris R, Van Overberge D, Dao-Thi M H, Poortmans F, Maene N, Wyns L
Laboratorium voor Ultrastructuur, Vrije Universiteit Brussel, Sint-Genesius-Rode, Belgium.
Proteins. 1994 Dec;20(4):330-46. doi: 10.1002/prot.340200406.
The structures of two crystal forms of lentil lectin are determined and refined at high resolution. Orthorhombic lentil lectin is refined at 1.80 A resolution to an R-factor of 0.184 and monoclinic lentil lectin at 1.75 A resolution to an R-factor of 0.175. These two structures are compared to each other and to the other available legume lectin structures. The monosaccharide binding pocket of each lectin monomer contains a tightly bound phosphate ion. This phosphate makes hydrogen bonding contacts with Asp-81 beta, Gly-99 beta, and Asn-125 beta, three residues that are highly conserved in most of the known legume lectin sequences and essential for monosaccharide recognition in all legume lectin crystal structures described thus far. A detailed analysis of the composition and properties of the hydrophobic contact network and hydrophobic nuclei in lentil lectin is presented. Contact map calculations reveal that dense clusters of nonpolar as well as polar side chains play a major role in secondary structure packing. This is illustrated by a large cluster of 24 mainly hydrophobic amino acids that is responsible for the majority of packing interactions between the two beta-sheets. Another series of four smaller and less hydrophobic clusters is found to mediate the packing of a number of loop structures upon the front sheet. A very dense, but not very conserved cluster is found to stabilize the transition metal binding site. The highly conserved and invariant nonpolar residues are distributed asymmetrically over the protein.
小扁豆凝集素两种晶体形式的结构已被确定并在高分辨率下进行了精修。正交晶系小扁豆凝集素在1.80埃分辨率下精修至R因子为0.184，单斜晶系小扁豆凝集素在1.75埃分辨率下精修至R因子为0.175。将这两种结构相互比较，并与其他可用的豆科植物凝集素结构进行比较。每个凝集素单体的单糖结合口袋中都含有一个紧密结合的磷酸根离子。该磷酸根与Asp-81β、Gly-99β和Asn-125β形成氢键，这三个残基在大多数已知的豆科植物凝集素序列中高度保守，并且对于迄今为止所描述的所有豆科植物凝集素晶体结构中的单糖识别至关重要。本文对小扁豆凝集素中疏水接触网络和疏水核的组成及性质进行了详细分析。接触图计算表明，非极性以及极性侧链的密集簇在二级结构堆积中起主要作用。这通过一大簇24个主要为疏水氨基酸得到说明，该簇负责两个β折叠之间的大部分堆积相互作用。发现另一系列四个较小且疏水性较弱的簇介导了前一个折叠上一些环结构的堆积。发现一个非常密集但不太保守的簇稳定了过渡金属结合位点。高度保守且不变的非极性残基在蛋白质上不对称分布。
