Unraveling the Knitted Sleeve

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Science  19 Nov 2004:
Vol. 306, Issue 5700, pp. 1261
DOI: 10.1126/science.306.5700.1261d

The surroundings in which membrane proteins reside consist of a hydrophobic interior (the fatty acid tails of phospholipids), a polar interfacial zone (the phospholipid head groups), and the aqueous compartments on either side of the bilayer. Rather than analyzing the energetics and dynamics of membrane protein insertion in the midst of such heterogeneity, Ganchev et al. have resorted to extracting peptides in a model membrane system. A shorter peptide and a longer one, both of which were previously shown to adopt a single-span α-helical conformation in membranes, and two phospholipids, one gel-like and one fluid, were mixed and probed by atomic force microscopy. Pulling (at a range of speeds) resulted in extraction of the peptide, at forces of about 90 pN applied to the gel-like mixture and only 60 pN for the more fluid membrane. A closer look at the resistance to extraction suggests that it arises primarily from the energy required for unwinding the first turn of the helix and dragging these residues from the hydrophobic interior into the interfacial region. — GJC

Biochemistry 10.1021/bi048372y (2004).

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