Many Pathways in Laboratory Evolution Can Lead to Improved Enzymes: How to Escape from Local Minima

Yosephine Gumulya, Joaquin Sanchis, Manfred T Reetz

Research output: Contribution to journalArticleResearchpeer-review

63 Citations (Scopus)

Abstract

Directed evolution is a method to tune the properties of enzymes for use in organic chemistry and biotechnology, to study enzyme mechanisms, and to shed light on Darwinian evolution in nature. In order to enhance its efficacy, iterative saturation mutagenesis (ISM) was implemented. This involves: 1) randomized mutation of appropriate sites of one or more residues; 2) screening of the initial mutant libraries for properties such as enzymatic rate, stereoselectivity, or thermal robustness; 3) use of the best hit in a given library as a template for saturation mutagenesis at the other sites; and 4) continuation of the process until the desired degree of enzyme improvement has been reached. Despite the success of a number of ISM-based studies, the question of the optimal choice of the many different possible pathways remains unanswered. Here we considered a complete 4-site ISM scheme. All 24 pathways were systematically explored, with the epoxide hydrolase from Aspergillus niger as the catalyst in the stereoselective hydrolytic kinetic resolution of a chiral epoxide. All 24 pathways were found to provide improved mutants with notably enhanced stereoselectivity. When a library failed to contain any hits, non-improved or even inferior mutants were used as templates in the continuation of the evolutionary pathway, thereby escaping from the local minimum. These observations have ramifications for directed evolution in general and for evolutionary biological studies in which protein engineering techniques are applied.

Original languageEnglish
Pages (from-to)1060-1066
Number of pages7
JournalChemBioChem
Volume13
Issue number7
DOIs
Publication statusPublished - 7 May 2012
Externally publishedYes

Keywords

  • Directed evolution
  • Enantioselectivity
  • Enzyme catalysis
  • Fitness landscapes
  • Iterative saturation mutagenesis

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