THE STRUCTURE OF HUMAN PANCREATIC ALPHA-AMYLASE AT 1.8 ANGSTROM RESOLUTION AND COMPARISONS WITH RELATED ENZYMES
THE STRUCTURE OF HUMAN PANCREATIC ALPHA-AMYLASE AT 1.8 ANGSTROM RESOLUTION AND COMPARISONS WITH RELATED ENZYMES
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DOI：
10.1002/pro.5560040908
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发表时间：
1995-09-01
期刊：
影响因子：
8
通讯作者：
WITHERS, SG
中科院分区：
文献类型：
--
作者：
BRAYER, GD;LUO, YG;WITHERS, SG
用x射线衍射技术测定了人胰腺α -淀粉酶的结构，其分辨率为1.8埃。这种酶被发现由三个结构域组成。最大的是结构域A（残基1-99、169-404），它形成一个中心的八链平行β -桶状结构，其一端是活性位点残基Asp 197、Glu 233和Asp 300。在这附近还发现了一个结合的氯离子，它与Arg 195、Asn 298和Arg 337形成配体相互作用。结构域B是最小的（残基100-168），用于在结构域a的β -桶壁上形成钙结合位点。与该钙进行配体相互作用的蛋白质基团包括Asn 100、Arg 158、Asp 167和His 201。结构域C（残基405-496）由反平行β结构组成，仅与结构域A和b松散相关。值得注意的是，人类胰腺α -淀粉酶的n端谷氨酰胺残基经过翻译后修饰，形成稳定的吡罗烷酮衍生物，可能对其他消化酶提供保护。基于结构的人胰腺α -淀粉酶与功能相关酶的比较强调了三点。首先，尽管这种方法促进了大量插入和缺失的初级序列比对，但总体而言，哺乳动物和真菌α -淀粉酶之间的序列同源性仅接近15%。其次，相比之下，这些相同的研究表明，显著的结构同源性是存在的，其顺序类似于70%。第三，结构域C的定位在α -淀粉酶之间有很大的不同。与猪的α -淀粉酶关系更为密切，其多肽链上有4个区域（237-250、304-310、346-354和458-461残基）与人类胰腺α -淀粉酶的构象明显不同。其中至少两种可能在这些酶之间观察到的底物差异和切割模式特异性中起作用。类似地，人类胰腺和唾液α -淀粉酶之间的氨基酸差异已经被定位，其中许多发生在活性位点附近。
The structure of human pancreatic alpha-amylase has been determined to 1.8 Angstrom resolution using X-ray diffraction techniques. This enzyme is found to be composed of three structural domains. The largest is Domain A (residues 1-99, 169-404), which forms a central eight-stranded parallel beta-barrel, to one end of which are located the active site residues Asp 197, Glu 233, and Asp 300. Also found in this vicinity is a bound chloride ion that forms ligand interactions to Arg 195, Asn 298, and Arg 337. Domain B is the smallest (residues 100-168) and serves to form a calcium binding site against the wall of the beta-barrel of Domain A. Protein groups making ligand interactions to this calcium include Asn 100, Arg 158, Asp 167, and His 201. Domain C (residues 405-496) is made up of anti-parallel beta-structure and is only loosely associated with Domains A and B. It is notable that the N-terminal glutamine residue of human pancreatic alpha-amylase undergoes a posttranslational modification to form a stable pyrrolidone derivative that may provide protection against other digestive enzymes. Structure-based comparisons of human pancreatic alpha-amylase with functionally related enzymes serve to emphasize three points. Firstly, despite this approach facilitating primary sequence alignments with respect to the numerous insertions and deletions present, overall there is only similar to 15% sequence homology between the mammalian and fungal alpha-amylases. Secondly, in contrast, these same studies indicate that significant structural homology is present and of the order of similar to 70%. Thirdly, the positioning of Domain C can vary considerably between alpha-amylases. In terms of the more closely related porcine enzyme, there are four regions of polypeptide chain (residues 237-250, 304-310, 346-354, and 458-461) with significantly different conformations from those in human pancreatic alpha-amylase. At least two of these could play a role in observed differential substrate and cleavage pattern specificities between these enzymes, Similarly, amino acid differences between human pancreatic and salivary alpha-amylases have been localized and a number of these occur in the vicinity of the active site.