Kossiakoff A A
Department of Pharmaceutical Chemistry, University of California, San Francisco 94143.
Science. 1988 Apr 8;240(4849):191-4. doi: 10.1126/science.3353715.
The protein deamidation process involves the conversion of the amide side-chain moieties of asparagine and glutamine residues to carboxyl groups. This conversion is an unusual form of protein modification in that it requires catalysis by an intramolecular reaction where both the substrate (asparagine and glutamine side chains) and "catalytic site" (the peptide nitrogen of the succeeding residue) are constituents of several consecutive residues along the polypeptide chain. The stereochemical factors governing this process were studied with a data base derived from the neutron crystallographic structure of trypsin from which amide groups and oxygen can be unambiguously differentiated because of their different neutron scattering properties. The neutron structure allowed for the direct determination of those residues that were deamidated; 3 of 13 asparagine residues were found to be modified. These modified residues were clearly distinguished by a distinct local conformation and hydrogen-bonding structure in contrast to those observed for the other asparagine residues. No correlation was found between preference to deamidate and the chemical character of residues flanking the site, as had been proposed from previous peptide studies.
蛋白质脱酰胺过程涉及天冬酰胺和谷氨酰胺残基的酰胺侧链部分向羧基的转化。这种转化是一种不寻常的蛋白质修饰形式，因为它需要通过分子内反应进行催化，其中底物（天冬酰胺和谷氨酰胺侧链）和“催化位点”（后续残基的肽氮）都是沿多肽链的几个连续残基的组成部分。利用从胰蛋白酶的中子晶体结构获得的数据库研究了控制这一过程的立体化学因素，由于酰胺基团和氧具有不同的中子散射特性，因此可以明确区分它们。中子结构使得能够直接确定那些被脱酰胺的残基；发现13个天冬酰胺残基中有3个被修饰。与其他天冬酰胺残基相比，这些修饰后的残基通过独特的局部构象和氢键结构明显区分开来。正如先前肽研究中所提出的那样，在脱酰胺偏好与位点侧翼残基的化学性质之间未发现相关性。
