Molybdate pumping into the molybdenum storage protein via an ATP-powered piercing mechanism.

ABSTRACT: The molybdenum storage protein (MoSto) deposits large amounts of molybdenum as polyoxomolybdate clusters in a heterohexameric (??)3 cage-like protein complex under ATP consumption. Here, we suggest a unique mechanism for the ATP-powered molybdate pumping process based on X-ray crystallography, cryoelectron microscopy, hydrogen-deuterium exchange mass spectrometry, and mutational studies of MoSto from Azotobacter vinelandii First, we show that molybdate, ATP, and Mg2+ consecutively bind into the open ATP-binding groove of the ?-subunit, which thereafter becomes tightly locked by fixing the previously disordered N-terminal arm of the ?-subunit over the ?-ATP. Next, we propose a nucleophilic attack of molybdate onto the ?-phosphate of ?-ATP, analogous to the similar reaction of the structurally related UMP kinase. The formed instable phosphoric-molybdic anhydride becomes immediately hydrolyzed and, according to the current data, the released and accelerated molybdate is pressed through the cage wall, presumably by turning aside the Met?149 side chain. A structural comparison between MoSto and UMP kinase provides valuable insight into how an enzyme is converted into a molecular machine during evolution. The postulated direct conversion of chemical energy into kinetic energy via an activating molybdate kinase and an exothermic pyrophosphatase reaction to overcome a proteinous barrier represents a novelty in ATP-fueled biochemistry, because normally, ATP hydrolysis initiates large-scale conformational changes to drive a distant process.

SUBMITTER: Brunle S 

PROVIDER: S-EPMC6936712 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature