The Latent Promiscuity of Newly Identified Microbial Lactonases Is Linked to a Recently Diverged Phosphotriesterase

Abstract

In essence, evolutionary processes occur gradually, while maintaining fitness throughout. Along this line, it has been proposed that the ability of a progenitor to promiscuously catalyze a low level of the evolving activity could facilitate the divergence of a new function by providing an immediate selective advantage. To directly establish a role for promiscuity in the divergence of natural enzymes, we attempted to trace the origins of a bacterial phosphotriesterase (PTE), an enzyme thought to have evolved for the purpose of degradation of a synthetic insecticide introduced in the 20th century. We surmised that PTE's promiscuous lactonase activity may be a vestige of its progenitor and tested homologues annotated as "putative PTEs" for lactonase and phosphotriesterase activity. We identified three genes that define a new group of microbial lactonases dubbed PTE-like lactonases (PLLs). These enzymes proficiently hydrolyze various lactones, and in particular quorum-sensing N-acyl homoserine lactones (AHLs), and exhibit much lower promiscuous phosphotriesterase activities. PLLs share key sequence and active site features with PTE and differ primarily by an insertion in one surface loop. Given their biochemical and biological function, PLLs are likely to have existed for many millions of years. PTE could have therefore evolved from a member of the PLL family while utilizing its latent promiscuous paraoxonase activity as an essential starting point.

Latent evolutionary potentials under the neutral mutational drift of an enzyme

“…Indeed, promiscuous activities were shown to comprise ample starting points in laboratory evolution experiments performed both in vitro (Khersonsky et al, 2006) and in vivo (Hall, 1999;Miller and Raines, 2005). There also exists evidence (which is inevitably indirect) indicating that promiscuity may have driven the divergence of new receptors (Bridgham et al, 2006) and enzymes (Afriat et al, 2006) in nature.…”

The enzymatic basis for pesticide bioremediation

“…Considering that organophosphate pesticides are synthetic compounds that have only existed in the environment since the 1950s, the rapid evolution of near diffusion-limited turnover rates in these enzymes is noteworthy. Recent work has shown that their likely evolutionary progenitor is a family of bacterial lactonases that exhibit lowlevel promiscuous phosphotriesterase activity [62].…”

Computational design of biological catalysts

“…Interestingly, no naturally occurring substrate has been identified for PTE. 5,6,11 An excellent model to illustrate the last case of promiscuity, product promiscuity, is g-humulene synthase, a sesquiterpene synthase that is known to produce 52 different sesquiterpenes from a sole substrate, farnesyl diphosphate, through a wide variety of cyclization mechanisms. The product distribution can be very sensitive to changes in specific amino acid residues.…”