F K Athappilly1, W A Hendrickson. 1. Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
Abstract
BACKGROUND: Acetyl-coenzyme A carboxylase catalyzes the first committed step of fatty acid biosynthesis. Universally, this reaction involves three functional components all related to a carboxybiotinyl intermediate. A biotinyl domain shuttles its covalently attached biotin prosthetic group between the active sites of a biotin carboxylase and a carboxyl transferase. In Escherichia coli, the three components reside in separate subunits: a biotinyl domain is the functional portion of one of these, biotin carboxy carrier protein (BCCP). RESULTS: We have expressed natural and selenomethionyl (Se-met) BCCP from E. coli as biotinylated recombinant proteins, proteolyzed them with subtilisin Carlsberg to produce the biotinyl domains BCCP and Se-met BCCPsc, determined the crystal structure of Se-met BCCPsc using a modified version of the multiwavelength anomalous diffraction (MAD) phasing protocol, and refined the structure for the natural BCCPsc at 1.8 A resolution. The structure may be described as a capped beta sandwich with quasi-dyad symmetry. Each half contains a characteristic hammerhead motif. The biotinylated lysin is located at a hairpin beta turn which connects the two symmetric halves of the molecule, and its biotinyl group interacts with a non-symmetric protrusion from the core. CONCLUSIONS: This first crystal structure of a biotinyl domain helps to unravel the central role of such domains in reactions catalyzed by biotin-dependent carboxylases. The hammerhead structure observed twice in BCCPsc may be regarded as the basic structural motif of biotinyl and lipoyl domains of a superfamily of enzymes. The new MAD phasing techniques developed in the course of determining this structure enhance the power of the MAD method.
BACKGROUND: Acetyl-coenzyme A carboxylase catalyzes the first committed step of fatty acid biosynthesis. Universally, this reaction involves three functional components all related to a carboxybiotinyl intermediate. A biotinyl domain shuttles its covalently attached biotin prosthetic group between the active sites of a biotin carboxylase and a carboxyl transferase. In Escherichia coli, the three components reside in separate subunits: a biotinyl domain is the functional portion of one of these, biotin carboxy carrier protein (BCCP). RESULTS: We have expressed natural and selenomethionyl (Se-met) BCCP from E. coli as biotinylated recombinant proteins, proteolyzed them with subtilisin Carlsberg to produce the biotinyl domains BCCP and Se-met BCCPsc, determined the crystal structure of Se-met BCCPsc using a modified version of the multiwavelength anomalous diffraction (MAD) phasing protocol, and refined the structure for the natural BCCPsc at 1.8 A resolution. The structure may be described as a capped beta sandwich with quasi-dyad symmetry. Each half contains a characteristic hammerhead motif. The biotinylated lysin is located at a hairpin beta turn which connects the two symmetric halves of the molecule, and its biotinyl group interacts with a non-symmetric protrusion from the core. CONCLUSIONS: This first crystal structure of a biotinyl domain helps to unravel the central role of such domains in reactions catalyzed by biotin-dependent carboxylases. The hammerhead structure observed twice in BCCPsc may be regarded as the basic structural motif of biotinyl and lipoyl domains of a superfamily of enzymes. The new MAD phasing techniques developed in the course of determining this structure enhance the power of the MAD method.
Authors: Matthew K Higgins; Evert Bokma; Eva Koronakis; Colin Hughes; Vassilis Koronakis Journal: Proc Natl Acad Sci U S A Date: 2004-06-28 Impact factor: 11.205
Authors: Tyler C Broussard; Matthew J Kobe; Svetlana Pakhomova; David B Neau; Amanda E Price; Tyler S Champion; Grover L Waldrop Journal: Structure Date: 2013-03-14 Impact factor: 5.006