In the journal Molecular Microbiology (January 2011), a National Institute of Dental and Craniofacial Research (NIDCR)-supported researcher and colleagues take another fascinating look at a previously unknown component of T forsythia's weaponry. It's a unique protease that they found encoded in T forsythia's genome and later named karilysin. Proteases are scissor-like enzymes that all forms of life use to snip specific cellular proteins and start, stop, or otherwise synchronize a range of biological activities. But microbes also secrete proteases as weapons, for instance, to degrade peptides that their host produces as a first line of defense against infection, called innate immunity. These pathogenic proteases, which poisonous snakes and insects also secrete in their venom, often belong to a family of enzymes called matrix metalloproteinases (MMPs). The researchers reported previously that karilysin closely resembles an MMP structurally. They also found that the protease inactivates the LL-37 antimicrobial peptide, suggesting one way that karilysin may contribute to chronic periodontitis. Now, they go further and elucidate the structure of one of karilysin's main catalytic domains, called Kly18, and take a remarkable turn into evolutionary biology. Comparing similar gene sequences across species, they found that the structure of Kly18 is evolutionarily much closer to the MMPs found in winged insects or mammals than those in bacteria. They concluded that the gene sequence encoding Kly18 must have been transferred from humans or another animal or insect to the bacterium, a biological phenomenon called horizontal gene transfer (HGT). "This proposed example of HGT entailing the shuffling of a metazoan [part of the animal kingdom] MMP to a human pathogenic bacterium, which involves distinct domains of life, is both a short circuit of Darwinian evolution and a testimony to the compatibility of proteins and cellular mechanisms despite evolutionary divergence over billions of years."
(Source: NIDCR, Science News in Brief, February 7, 2011)