The Role of Tryptophan Residues in the Function and Stability of the Mechanosensitive Channel MscS from Escherichia coli

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• 作者：Akiko Rasmussen ; Tim Rasmussen ; Michelle D. Edwards ; Daniela Schauer ; Ulrike Schumann ; Samantha Miller ; Ian R. Booth
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：September 25, 2007
• 年：2007
• 卷：46
• 期：38
• 页码：10899 - 10908
• 全文大小：405K
• 年卷期：v.46,no.38(September 25, 2007)
• ISSN：1520-4995

文摘

Tryptophan (Trp) residues play important roles in many proteins. In particular they are enrichedin protein surfaces involved in protein docking and are often found in membrane proteins close to thelipid head groups. However, they are usually absent from the membrane domains of mechanosensitivechannels. Three Trp residues occur naturally in the Escherichia coli MscS (MscS-Ec) protein: W16 liesin the periplasm, immediately before the first transmembrane span (TM1), whereas W240 and W251 lieat the subunit interfaces that create the cytoplasmic vestibule portals. The role of these residues in MscSfunction and stability were investigated using site-directed mutagenesis. Functional channels with alteredproperties were created when any of the Trp residues were replaced by another amino acid, with thegreatest retention of function associated with phenylalanine (Phe) substitutions. Analysis of the fluorescenceproperties of purified mutant MscS proteins containing single Trp residues revealed that W16 and W251are relatively inaccessible, whereas W240 is accessible to quenching agents. The data point to a significantrole for W16 in the gating of MscS, and an essential role for W240 in MscS oligomer stability.