Interfacial polar interactions affect gramicidin channel kinetics
Tatiana K. Rostovtseva 1*, Horia I. Petrache 2, Namdar Kazemi 1, Elnaz Hassanzadeh 1 and Sergey M. Bezrukov 1
1 LPSB/NICHD, NIH
2 Indiana University Purdue University Indianapolis
* To whom correspondence should be addressed. E-mail: rostovtt{at}mail.nih.gov.
Submitted on August 28, 2007
Revised on November 3, 2007
Accepted on 20 November 2007
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Abstract |
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Critical to biological processes such as secretion and transport, protein-lipid interactions within the membrane and at the membrane-water interface still raise many questions. Here we examine the role of lipid headgroups in these interactions by using gramicidin A (gA) channels in planar bilayers as a probe. We show that while headgroup demethylation from phosphatidylcholine (DOPC) to phosphatidylethanolamine (DOPE) decreases the lifetime of gA channels by an order of magnitude in accordance with the currently accepted hydrophobic mismatching mechanism, our findings with diether-DOPC suggest the importance of the headgroup-peptide interactions. According to our x-ray diffraction measurements, this lipid has the same hydrophobic thickness as DOPC but increases gA lifetime by a factor of 2. Thus we demonstrate that peptide-headgroup interactions may dominate over the effect of hydrophobic mismatch in regulating protein function.
Key Words:
channel lifetime, hydrophobic mismatching, lipid headgroups, planar lipid membrane, x-ray diffraction
