Characterization of molecular mechanism of electrogenic transporters accompanying ion movement

为了阐明伴随离子运动的电致转运体的分子机制，我们精确测定了盐紫红质、光驱动Cl-泵（pHR）和人寡肽转运体（hPEPT1）的转运。(1) pHR的晶体结构（PDB:3QBG）清楚地表明，氨基酸残基Ser 130位于质子化的席夫碱附近，并与席夫花瓶形成氢键。根据突变体Ser130的Cl-转运活性，发现Ser130与PBS配合，在阴离子转运循环中起到抑制Cl-内漏、反流的分子阀作用。(2)我们证明了PEPT1中位于His57附近的Ser302突变导致了运输活性中最佳pH值的碱性转移。这种转变表明，Ser302的羟基与His57的咪唑形成氢键，可能在生理肠道pH范围内保持最佳的摄取活性。

To clarify the molecular mechanism of the electrogenic transporter accompanying ion movement, we precisely determined the transport of halorhodopsin, a light-driven Cl- pump (pHR) and human oligopeptide transporter (hPEPT1).(1) The crystal structure (PDB:3QBG) of pHR clearly shows that the amino acid residue, Ser 130 is located in the vicinity of the protonated Schiff base and forms the hydrogen bond to the Schiff vase. Based on the Cl- transport activities of mutant Ser130, it has turned out that Ser130 coordinates with PBS and functions as a molecular valve to hinder the internal leak, backflux of Cl- during anion-transport cycle.(2) We demonstrated that mutation of Ser302 located in the vicinity of His57 in PEPT1 caused the alkaline shift of the optimum pH in the transport activity. This shift demonstrates that the hydroxyl group of Ser302 forms the hydrogen-bonding with the imidazole of His57, which might keep the uptake activity optimum in the range of physiological intestinal pH.