Slow alpha helix formation during folding of a membrane protein

TY - JOUR

T1 - Slow alpha helix formation during folding of a membrane protein

AU - Riley, M L

AU - Wallace, B A

AU - Flitsch, S L

AU - Booth, P J

PY - 1997/1/7

Y1 - 1997/1/7

N2 - Very little is known about the folding of proteins within biological membranes. A "two-stage" model has been proposed on thermodynamic grounds for the folding of alpha helical, integral membrane proteins, the first stage of which involves formation of transmembrane alpha helices that are proposed to behave as autonomous folding domains. Here, we investigate alpha helix formation in bacteriorhodopsin and present a time-resolved circular dichroism study of the slow in vitro folding of this protein. We show that, although some of the protein's alpha helices form early, a significant part of the protein's secondary structure appears to form late in the folding process. Over 30 amino acids, equivalent to at least one of bacteriorhodopsin's seven transmembrane segments, slowly fold from disordered structures to alpha helices with an apparent rate constant of about 0.012 s-1 at pH 6 or 0.0077 s-1 at pH 8. This is a rate-limiting step in protein folding, which is dependent on the pH and the composition of the lipid bilayer.

AB - Very little is known about the folding of proteins within biological membranes. A "two-stage" model has been proposed on thermodynamic grounds for the folding of alpha helical, integral membrane proteins, the first stage of which involves formation of transmembrane alpha helices that are proposed to behave as autonomous folding domains. Here, we investigate alpha helix formation in bacteriorhodopsin and present a time-resolved circular dichroism study of the slow in vitro folding of this protein. We show that, although some of the protein's alpha helices form early, a significant part of the protein's secondary structure appears to form late in the folding process. Over 30 amino acids, equivalent to at least one of bacteriorhodopsin's seven transmembrane segments, slowly fold from disordered structures to alpha helices with an apparent rate constant of about 0.012 s-1 at pH 6 or 0.0077 s-1 at pH 8. This is a rate-limiting step in protein folding, which is dependent on the pH and the composition of the lipid bilayer.

KW - Bacteriorhodopsins

KW - Circular Dichroism

KW - Dimyristoylphosphatidylcholine

KW - Fluorometry

KW - Hydrogen-Ion Concentration

KW - Kinetics

KW - Liposomes

KW - Membrane Proteins

KW - Models, Chemical

KW - Phospholipid Ethers

KW - Protein Denaturation

KW - Protein Folding

KW - Protein Structure, Secondary

KW - Thermodynamics

U2 - 10.1021/bi962199r

DO - 10.1021/bi962199r

M3 - Article

C2 - 8993333

SN - 0006-2960

VL - 36

SP - 192

EP - 196

JO - Biochemistry

JF - Biochemistry

IS - 1

ER -