James Gumbart and Klaus Schulten. The roles of pore ring and plug in the SecY protein-conducting channel. Journal of General Physiology, 132:709-719, 2008. (PMC: 2585858)

GUMB2008 The protein-conducting channel, or translocon, is an evolutionarily conserved complex which allows nascent proteins to cross a cellular membrane or integrate into it. The crystal structure of an archaeal translocon, the SecY complex, revealed that two elements contribute to sealing the channel: a small “plug” domain blocking the periplasmic region of the channel and a pore ring composed of six hydrophobic residues acting as a constriction point at the channel’s center. In order to determine the independent functions of these two elements, we have performed molecular dynamics simulations of the native channel as well as of two recently structurally resolved mutants in which portions of their plugs were deleted. We find that in the mutants, the instability in the plug region leads to a comcomitant increase in flexibility of the pore ring. The instability is quantified by the rate of water permeation in each system, as well as by the force required for oligopeptide translocation. Through a novel simulation in which the interactions between the plug and water were independently controlled, we find that the role of the plug in stabilizing the pore ring is significantly more important than its role as a purely steric barrier.


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