Inverse heavy enzyme isotope effects in methylthioadenosine nucleosidases

Morais Brown, Ioanna Zoi, Dimitri Antoniou, Hilda A. Namanja-Magliano, Steven D. Schwartz, Vern L. Schramm

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Heavy enzyme isotope effects occur in proteins substituted with 2H-, 13C-, and 15N-enriched amino acids. Mass alterations perturb femtosecond protein motions and have been used to study the linkage between fast motions and transition-state barrier crossing. Heavy enzymes typically show slower rates for their chemical steps. Heavy bacterial methylthioadenosine nucleosidases (MTANs from Helicobactor pylori and Escherichia coli) gave normal isotope effects in steady-state kinetics, with slower rates for the heavy enzymes. However, both enzymes revealed rare inverse isotope effects on their chemical steps, with faster chemical steps in the heavy enzymes. Computational transition-path sampling studies of H. pylori and E. coli MTANs indicated closer enzyme–reactant interactions in the heavy MTANs at times near the transition state, resulting in an improved reaction coordinate geometry. Specific catalytic interactions more favorable for heavy MTANs include improved contacts to the catalytic water nucleophile and to the adenine leaving group. Heavy bacterial MTANs depart from other heavy enzymes as slowed vibrational modes from the heavy isotope substitution caused improved barrier-crossing efficiency. Improved sampling frequency and reactant coordinate distances are highlighted as key factors in MTAN transition-state stabilization.

Original languageEnglish (US)
Article numbere2109118118
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number40
StatePublished - Oct 5 2021


  • Femtosecond protein dynamics
  • Isotope-substituted protein
  • MTAN
  • Transition-path sampling
  • Transition-state formation

ASJC Scopus subject areas

  • General


Dive into the research topics of 'Inverse heavy enzyme isotope effects in methylthioadenosine nucleosidases'. Together they form a unique fingerprint.

Cite this