Pajor A M, Krajewski S J, Sun N, Gangula R
Department of Physiology, University of Texas Medical Branch, Galveston, TX 77555-0641, USA.
Biochem J. 1999 Nov 15;344 Pt 1(Pt 1):205-9.
The role of cysteine residues in the Na(+)/dicarboxylate co-transporter (NaDC-1) was tested using site-directed mutagenesis. The transport activity of NaDC-1 was not affected by mutagenesis of any of the 11 cysteine residues, indicating that no individual cysteine residue is necessary for function. NaDC-1 is sensitive to inhibition by the impermeant cysteine-specific reagent, p-chloromercuribenzenesulphonate (pCMBS). The pCMBS-sensitive residues in NaDC-1 are Cys-227, found in transmembrane domain 5, and Cys-476, located in transmembrane domain 9. Although cysteine residues are not required for function in NaDC-1, their presence appears to be important for protein stability or trafficking to the plasma membrane. There was a direct relationship between the number of cysteine residues, regardless of location, and the transport activity and expression of NaDC-1. The results indicate that mutagenesis of multiple cysteine residues in NaDC-1 may alter the shape or configuration of the protein, leading to alterations in protein trafficking or stability.
利用定点诱变技术检测了半胱氨酸残基在钠/二羧酸共转运蛋白（NaDC-1）中的作用。11个半胱氨酸残基中的任何一个发生诱变，NaDC-1的转运活性均不受影响，这表明单个半胱氨酸残基对其功能并非必需。NaDC-1对非渗透性半胱氨酸特异性试剂对氯汞苯磺酸盐（pCMBS）的抑制作用敏感。NaDC-1中对pCMBS敏感的残基是位于跨膜结构域5的半胱氨酸-227和位于跨膜结构域9的半胱氨酸-476。虽然半胱氨酸残基对NaDC-1的功能并非必需，但它们的存在似乎对蛋白质稳定性或向质膜的转运很重要。无论位置如何，半胱氨酸残基的数量与NaDC-1的转运活性和表达之间存在直接关系。结果表明，NaDC-1中多个半胱氨酸残基的诱变可能会改变蛋白质的形状或构象，从而导致蛋白质转运或稳定性的改变。
