Abstract
Surface localized microbial enolases’ binding with human plasminogen has been increasingly proven to have an important role in initial infection cycle of several human pathogens. Likewise, surface localized Mycobacterium tuberculosis (Mtb) enolase also binds to human plasminogen, and this interaction may entail crucial consequences for granuloma stability. The current study is the first attempt to explore the plasminogen interacting residues of enolase from Mtb. Beginning with the structural modeling of Mtb enolase, the binding pose of Mtb enolase and human plasminogen was predicted using protein‐protein docking simulations. The binding pose revealed the interface region with interacting residues and molecular interactions. Next, the interacting residues were refined and ranked by using various criteria. Finally, the selected interacting residues were tested experimentally for their involvement in plasminogen binding. The two consecutive lysine residues, Lys‐193 and Lys‐194, turned out to be active residues for plasminogen binding. These residues when substituted for alanine along with the most active residue Lys‐429, that is, the triple mutant (K193A + K194A + K429A) Mtb enolase, exhibited 40% reduction in plasminogen binding. It is worth noting that Mtb enolase lost nearly half of the plasminogen binding activity with only three simultaneous substitutions, without any significant secondary structure perturbation. Further, the sequence comparison between Mtb and human enolase isoforms suggests the possibility of selective targeting of Mtb enolase to obstruct binding of human plasminogen.
Current work aims at exploring the role of enolase present on Mtb's cell surface in interaction with the host's plasminogen. Further, using various suitable computational methods the key amino acid residues involved in this event have been predicted and then mutated singly as well as in combinantions to confirm their engagement in plasminogen binding. Plasminogen being a major matrix protein of the host tissues is exploited by several pathogens as a proteolytic tool after being activated to the Plasmin which is a broad spectrum protease.