title: Stability and solvent accessibility of SecA protein of Escherichia coli.
abstract: It has been shown that many proteins, when converted into partially unfolded structures, interact strongly with a lipid bilayer. SecA protein of Escherichia coli is an unusual water-soluble protein which, in the native form, can readily penetrate the membrane and lipid bilayer. In order to see whether the native SecA exhibits partially unfolded characteristics, the stability and solvent accessibility of SecA were studied using various spectroscopic and hydrogen-exchange methods. The results are compared with the reported data for native and molten globule forms of alpha-lactalbumin (alpha-LA), as well as those for apocytochrome c. The exposure of hydrophobic residues of SecA, as monitored by 8-anilinonaphthalene-1-sulfonic acid (ANS) binding, and the extent of amide hydrogen exchange were comparable to those of native alpha-LA. On the other hand, equilibrium unfolding experiments showed that SecA is less stable than native alpha-LA. The results of tryptic digestion and the change of endogenous ATPase activity induced by guanidine hydrochloride were suggestive of the C-terminal half of SecA being more flexible than the rest of the protein. The overall conclusion is that the SecA as a whole has a somewhat open structure due to a relatively unstable C-domain which may facilitate its penetration into a lipid bilayer.
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Taejon.
authors.forename: M
authors.initials: M
authors.lastname: Song
authors.forename: H
authors.initials: H
authors.lastname: Kim
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D000817:Anilino Naphthalenesulfonates; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; D019791:Guanidine / Q000494:pharmacology; D006859:Hydrogen; D006868:Hydrolysis; D026901:Membrane Transport Proteins; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014316:Tritium; D014357:Trypsin
chemical_list: D000817:Anilino Naphthalenesulfonates; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D012997:Solvents; D014316:Tritium; C027132:1-anilino-8-naphthalenesulfonate; D006859:Hydrogen; D014357:Trypsin; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins; D019791:Guanidine