Yother J, Briles D E
Department of Microbiology, University of Alabama, Birmingham 35294.
J Bacteriol. 1992 Jan;174(2):601-9. doi: 10.1128/jb.174.2.601-609.1992.
Analysis of the sequence for the gene encoding PspA (pneumococcal surface protein A) of Streptococcus pneumoniae revealed the presence of four distinct domains in the mature protein. The structure of the N-terminal half of PspA was highly consistent with that of an alpha-helical coiled-coil protein. The alpha-helical domain was followed by a proline-rich domain (with two regions in which 18 of 43 and 5 of 11 of the residues are prolines) and a repeat domain consisting of 10 highly conserved 20-amino-acid repeats. A fourth domain consisting of a hydrophobic region too short to serve as a membrane anchor and a poorly charged region followed the repeats and preceded the translation stop codon. The C-terminal region of PspA did not possess features conserved among numerous other surface proteins, suggesting that PspA is attached to the cell by a mechanism unique among known surface proteins of gram-positive bacteria. The repeat domain of PspA was found to have significant homology with C-terminal repeat regions of proteins from Streptococcus mutans, Streptococcus downei, Clostridium difficile, and S. pneumoniae. Comparisons of these regions with respect to functions and homologies suggested that, through evolution, the repeat regions may have lost or gained a mechanism for attachment to the bacterial cell.
对肺炎链球菌编码PspA（肺炎球菌表面蛋白A）的基因序列分析显示，成熟蛋白中存在四个不同的结构域。PspA N端一半的结构与α-螺旋卷曲螺旋蛋白高度一致。α-螺旋结构域之后是富含脯氨酸的结构域（有两个区域，其中43个残基中有18个、11个残基中有5个是脯氨酸）和一个由10个高度保守的20个氨基酸重复序列组成的重复结构域。第四个结构域由一个太短而不能作为膜锚定的疏水区域和一个电荷较少的区域组成，位于重复序列之后、翻译终止密码子之前。PspA的C端区域不具备许多其他表面蛋白中保守的特征，这表明PspA通过革兰氏阳性菌已知表面蛋白中独特的机制附着于细胞。发现PspA的重复结构域与变形链球菌、唐氏链球菌、艰难梭菌和肺炎链球菌的蛋白C端重复区域有显著同源性。对这些区域在功能和同源性方面的比较表明，通过进化，重复区域可能已经失去或获得了一种附着于细菌细胞的机制。
