ROLE OF CONSERVED RESIDUES OF CsrABb IN THE PATHOPHYSIOLOGY OF Borrelia burgdorferi

Carbon storage regulator A is an RNA binding protein that has been characterized in many bacterial species to play a central regulatory role by modulating several metabolic processes. We recently showed that a homolog of CsrA in B. burgdorferi (CsrABb, BB0184) was up-regulated in response to propagation of B. burgdorferi under mammalian host-specific conditions and has been characterized to alter levels of key regulators of gene expression and pathogenesis related proteins of B. burgdorferi. Sequence analysis of CsrABb revealed the presence of two domains with several conserved residues that are known to interact with small RNA molecules in other bacterial systems. In order delineate the role of these residues, we generated site-specific mutants replacing the conserved amino acid residues with alanines. We transformed B. burgdorferi with plasmids containing a native copy CsrABb/L2A-V-L4A-S-R6A-K7A-------I40A-K-I42A-F-R44A-I47A (RR59) substitutions that will facilitate homologous recombination and isolated mutants by counter selection with gentamicin. Similarly, we transformed B. burgdorferi with a plasmid containing a native copy CsrABb lacking the C-terminal 7 amino acid residues of CsrABb (RR66) that is unique to B.burgdorferi. Immunoblot analysis with anti-CsrABb serum demonstrated that levels of CsrA expression were significantly elevated in RR59, along with the levels of OspC, RpoS, BosR, BBA34. However levels of P66, expression were found increased in RR66. We are in the process of determining if these changes will alter the levels of expression of other regulators and pathogenesis related proteins of B. burgdorferi. The further characterization of molecular basis of regulation mediated by CsrABb will provide significant insights into the patho-physiology of B. burgdorferi.