Nucleotide Binding to ARL2 in the TBCD.ARL2.beta-Tubulin Complex Drives Conformational Changes in beta-Tubulin

作者：Francis Joshua W; Goswami Devrishi; Novick Scott J; Pascal Bruce D; Weikum Emily R; Ortlund Eric A; Griffin Patrick R; Kahn Richard A^*

来源：Journal of Molecular Biology, 2017, 429(23): 3696-3716.

DOI：10.1016/j.jmb.2017.09.016

• GTPase
• ARL2
• TBCD
• Cofactor D
• Tubulin

Microtubules are highly dynamic tubulin polymers that are required for a variety of cellular functions. Despite the importance of a cellular population of tubulin dimers, we have incomplete information about the mechanisms involved in the biogenesis of alpha beta-tubulin heterodimers. In addition to prefoldin and the TCP-1 Ring Complex, five tubulin-specific chaperones, termed cofactors A-E (TBCA-E), and GTP are required for the folding of alpha- and beta-tubulin subunits and assembly into heterodimers. We recently described the purification of a novel trimer, TBCD.ARL2.beta-tubulin. Here, we employed hydrogen/deuterium exchange coupled with mass spectrometry to explore the dynamics of each of the proteins in the trimer. Addition of guanine nucleotides resulted in changes in the solvent accessibility of regions of each protein that led to predictions about each's role in tubulin folding. Initial testing of that model confirmed that it is ARL2, and not beta-tubulin, that exchanges GTP in the trimer. Comparisons of the dynamics of ARL2 monomer to ARL2 in the trimer suggested that its protein interactions were comparable to those of a canonical GTPase with an effector. This was supported by the use of nucleotide-binding assays that revealed an increase in the affinity for GTP by ARL2 in the trimer. We conclude that the TBCD.ARL2.beta-tubulin complex represents a functional intermediate in the beta-tubulin folding pathway whose activity is regulated by the cycling of nucleotides on ARL2. The co-purification of guanine nucleotide on the beta-tubulin in the trimer is also shown, with implications to modeling the pathway.

• 出版日期2017-11-24