Pathway of oxidative folding of alpha-lactalbumin: a model for illustrating the diversity of disulfide folding pathways.
The pathway of oxidative folding of alpha-lactalbumin (alpha LA) (four disulfide bonds) has been characterized by structural and kinetic analysis of the acid-trapped folding intermediates. In the absence of calcium, oxidative folding of alpha LA proceeds through highly heterogeneous species of one-, two-, three-, and four-disulfide (scrambled) intermediates to reach the native structure. In the presence of calcium, the folding intermediates of alpha LA comprise two predominant isomers (alpha LA-IIA and alpha LA-IIIA) adopting exclusively native disulfide bonds, including the two disulfide bonds (Cys(61)-Cys(77) and Cys(73)-Cys(91)) located within the beta-sheet calcium binding domain. alpha LA-IIA is a two-disulfide species consisting of Cys(61)-Cys(77) and Cys(73)-Cys(91) disulfide bonds. alpha LA-IIIA contains Cys(61)-Cys(77), Cys(73)-Cys(91), and Cys(28)-Cys(111) disulfide bonds. The underlying mechanism of the contrasting folding pathways of calcium-bound and calcium-depleted alpha LA is congruent with the cause of diversity of disulfide folding pathways observed among many well-characterized three-disulfide proteins, including bovine pancreatic trypsin inhibitor and hirudin. Our study also reveals novel aspects of the folding mechanism of alpha LA that have not been described previously.
Chang
Jui-Yoa
JY
Research Center for Protein Chemistry, Institute of Molecular Medicine and Department of Biochemistry and Molecular Biology, The University of Texas, Houston, Texas 77030, USA. Rowan.Chang@uth.tmc.edu
Li
Li
L
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism*; D007536:Isomerism; D007700:Kinetics; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D017510:Protein Folding
D004220:Disulfides; D007768:Lactalbumin