Inactivation and Site-specific Oxidation of Aquatic Extracellular Bacterial Leucine Aminopeptidase by Singlet Oxygen

Extracellular enzymes are master recyclers of organic matter, and to predict their functional lifetime, we need to understand their environmental transformation processes. In surface waters, direct and indirect photochemical transformation is a known driver of inactivation. We investigated molecular...

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Bibliographic Details
Published in:Environmental science & technology 2020-11, Vol.54 (22), p.14403-14412
Main Authors: Egli, Christine M, Stravs, Michael A, Janssen, Elisabeth M. L
Format: Article
Language:English
Subjects:
Accessibility
Amino Acids
Aminopeptidase
Contaminants in Aquatic and Terrestrial Environments
Deactivation
Enzymes
Extracellular enzymes
Histidine
Inactivation
Kinetics
Leucine
Leucyl Aminopeptidase
Organic matter
Oxidants
Oxidation
Oxidation rate
Oxidation-Reduction
Oxidizing agents
Oxygen
Photochemicals
Proteins
Rate constants
Reaction kinetics
Singlet Oxygen
Surface water
Transformations
Tryptophan
Zinc coordination
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Summary:Extracellular enzymes are master recyclers of organic matter, and to predict their functional lifetime, we need to understand their environmental transformation processes. In surface waters, direct and indirect photochemical transformation is a known driver of inactivation. We investigated molecular changes that occur along with inactivation in aminopeptidase, an abundant class of extracellular enzymes. We studied the inactivation kinetics and localized oxidation caused by singlet oxygen, 1O2, a major photochemically derived oxidant toward amino acids. Aminopeptidase showed second-order inactivation rate constants with 1O2 comparable to those of free amino acids. We then visualized site-specific oxidation kinetics within the three-dimensional protein and demonstrated that fastest oxidation occurred around the active site and at other reactive amino acids. However, second-order oxidation rate constants did not correlate strictly with the 1O2-accessible surface areas of those amino acids. We inspected site-specific processes by a comprehensive suspect screening for 723,288 possible transformation products. We concluded that histidine involved in zinc coordination at the active site reacted slower than what was expected by its accessibility, and we differentiated between two competing reaction pathways of 1O2 with tryptophan residues. This systematic analysis can be directly applied to other proteins and transformation reactions.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.0c04696