5vt9

Publication Abstract from PubMed

Apicomplexan parasites such as Toxoplasma gondii rely on a unique form of locomotion known as gliding motility. Generating the mechanical forces to support motility are divergent class XIV myosins (MyoA) coordinated by accessory proteins known as light chains. While the importance of the MyoA-light chain complex is well established, the detailed mechanisms governing its assembly and regulation are relatively unknown. To establish a molecular blueprint of this dynamic complex, we first mapped the adjacent binding sites of light chains MLC1 and ELC1 on the MyoA neck (residues 775-818) using a combination of hydrogen-deuterium exchange mass spectrometry (HDX-MS) and isothermal titration calorimetry (ITC). We then determined the 1.85 A resolution crystal structure of MLC1 in complex with its cognate MyoA peptide. Structural analysis revealed a bi-lobed architecture with MLC1 clamping tightly around the helical MyoA peptide, consistent with the stable 10nM Kd measured by ITC. We next showed that coordination of calcium by an EF-hand in ELC1, and prebinding of MLC1 to the MyoA neck, enhanced the affinity of ELC1 for the MyoA neck 7 and 8 fold, respectively. When combined, these factors enhanced ELC1 binding 49 fold (to a Kd of 12nM). Using the full length MyoA motor (residues 1-831), we then showed that, in addition to coordinating the neck region, ELC1 appears to engage the MyoA converter sub-domain, which couples the motor domain to the neck. These data support an assembly model where staged binding events cooperate to yield high affinity complexes that are able to maximize force transduction.

Dissecting the molecular assembly of the Toxoplasma gondii MyoA motility complex.,Powell CJ, Jenkins ML, Parker ML, Ramaswamy R, Kelsen A, Warshaw DM, Ward GE, Burke JE, Boulanger MJ J Biol Chem. 2017 Sep 25. pii: jbc.M117.809632. doi: 10.1074/jbc.M117.809632. PMID:28972141^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.