Parker, Christine H2; Morgan, Christopher R3; Rand, Kasper Dyrberg4; Engen, John R3; Jorgenson, James W3; Stafford, Darrel W3
1 Analytical Biosciences, Department of Pharmacy, Faculty of Health and Medical Sciences, Københavns Universitet2 Department of Chemistry and ‡Department of Biology, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.3 unknown4 Analytical Biosciences, Department of Pharmacy, Faculty of Health and Medical Sciences, Københavns Universitet
Gamma (γ)-glutamyl carboxylase (GGCX) is an integral membrane protein responsible for the post-translational catalytic conversion of select glutamic acid (Glu) residues to γ-carboxy glutamic acid (Gla) in vitamin K-dependent (VKD) proteins. Understanding the mechanism of carboxylation and the role of GGCX in the vitamin K cycle is of biological interest in the development of therapeutics for blood coagulation disorders. Historically, biophysical investigations and structural characterizations of GGCX have been limited due to complexities involving the availability of an appropriate model membrane system. In previous work, a hydrogen exchange mass spectrometry (HX MS) platform was developed to study the structural configuration of GGCX in a near-native nanodisc phospholipid environment. Here we have applied the nanodisc-HX MS approach to characterize specific domains of GGCX that exhibit structural rearrangements upon binding the high-affinity consensus propeptide (pCon; AVFLSREQANQVLQRRRR). pCon binding was shown to be specific for monomeric GGCX-nanodiscs and promoted enhanced structural stability to the nanodisc-integrated complex while maintaining catalytic activity in the presence of carboxylation co-substrates. Noteworthy modifications in HX of GGCX were prominently observed in GGCX peptides 491-507 and 395-401 upon pCon association, consistent with regions previously identified as sites for propeptide and glutamate binding. Several additional protein regions exhibited minor gains in solvent protection upon propeptide incorporation, providing evidence for a structural reorientation of the GGCX complex in association with VKD carboxylation. The results herein demonstrate that nanodisc-HX MS can be utilized to study molecular interactions of membrane-bound enzymes in the absence of a complete three-dimensional structure and to map dynamic rearrangements induced upon ligand binding.
Biochemistry, 2014, Vol 53, Issue 9, p. 1511-20
Carbon-Carbon Ligases; Humans; Hydrogen; Mass Spectrometry; Peptides; Protein Binding; Protein Conformation