Amide hydrogen exchange shows that malate dehydrogenase is a folded monomer at pH 5

Chen, JW Smith, DL

Jw. Chen et Dl. Smith, Amide hydrogen exchange shows that malate dehydrogenase is a folded monomer at pH 5, PROTEIN SCI, 10(5), 2001, pp. 1079-1083

27

INGLESE

Article

Biochemistry & Biophysics

PROTEIN SCIENCE

0961-8368 → ACNP

10

5

2001

1079 - 1083

ISI

0961-8368(200105)10:5<1079:AHESTM>2.0.ZU;2-6

Although there is general agreement that native mitochondrial malate dehydr ogenase (MDH) exists as a dimer at pH 7, its aggregation state at pH 5 is l ess certain. The present amide hydrogen exchange study was performed to det ermine whether MDH remains a dimer at pH 5. To detect pH-induced changes in solvent accessibility, MDH was exposed to D2O at pH 5 or 7, then fragmente d with pepsin into peptides that were analyzed by mass spectrometry. Even a fter adjustments for the effect of pH on the intrinsic rate of hydrogen exc hange, large increases in deuterium levels were found at pH 5 only in pepti c fragments derived from the subunit binding surface of MDH. In parallel ex periments, elevated deuterium levels were also found in the same regions of MDH monomer trapped inside a mutant form of the chaperonin GroEL. This sel ective increase in hydrogen exchange rates, which was attributed to increas ed solvent accessibility of these regions, provides new evidence that MDH i s a monomer at pH 5.