title: Phenylalanine-rich peptides potently bind ESAT6, a virulence determinant of Mycobacterium tuberculosis, and concurrently affect the pathogen's growth.
abstract: BACKGROUND
  The secretory proteins of Mycobacterium tuberculosis (M. tuberculosis) have been known to be involved in the virulence, pathogenesis as well as proliferation of the pathogen. Among this set, many proteins have been hypothesized to play a critical role at the genesis of the onset of infection, the primary site of which is invariably the human lung.
  
  
  RESULTS
  During our efforts to isolate potential binding partners of key secretory proteins of M. tuberculosis from a human lung protein library, we isolated peptides that strongly bound the virulence determinant protein Esat6. All peptides were less than fifty amino acids in length and the binding was confirmed by in vivo as well as in vitro studies. Curiously, we found all three binders to be unusually rich in phenylalanine, with one of the three peptides a short fragment of the human cytochrome c oxidase-3 (Cox-3). The most accessible of the three binders, named Hcl1, was shown also to bind to the Mycobacterium smegmatis (M. smegmatis) Esat6 homologue. Expression of hcl1 in M. tuberculosis H37Rv led to considerable reduction in growth. Microarray analysis showed that Hcl1 affects a host of key cellular pathways in M. tuberculosis. In a macrophage infection model, the sets expressing hcl1 were shown to clear off M. tuberculosis in much greater numbers than those infected macrophages wherein the M. tuberculosis was not expressing the peptide. Transmission electron microscopy studies of hcl1 expressing M. tuberculosis showed prominent expulsion of cellular material into the matrix, hinting at cell wall damage.
  
  
  CONCLUSIONS
  While the debilitating effects of Hcl1 on M. tuberculosis are unrelated and not because of the peptide's binding to Esat6-as the latter is not an essential protein of M. tuberculosis-nonetheless, further studies with this peptide, as well as a closer inspection of the microarray data may shed important light on the suitability of such small phenylalanine-rich peptides as potential drug-like molecules against this pathogen.
authors.affiliation: Recombinant Gene Products Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India.
authors.forename: Krishan
authors.initials: K
authors.lastname: Kumar
authors.forename: Megha
authors.initials: M
authors.lastname: Tharad
authors.forename: Swetha
authors.initials: S
authors.lastname: Ganapathy
authors.forename: Geeta
authors.initials: G
authors.lastname: Ram
authors.forename: Azeet
authors.initials: A
authors.lastname: Narayan
authors.forename: Jameel Ahmad
authors.initials: JA
authors.lastname: Khan
authors.forename: Rana
authors.initials: R
authors.lastname: Pratap
authors.forename: Anamika
authors.initials: A
authors.lastname: Ghosh
authors.forename: Sachin Kumar
authors.initials: SK
authors.lastname: Samuchiwal
authors.forename: Sushil
authors.initials: S
authors.lastname: Kumar
authors.forename: Kuhulika
authors.initials: K
authors.lastname: Bhalla
authors.forename: Deepti
authors.initials: D
authors.lastname: Gupta
authors.forename: Krishnamurthy
authors.initials: K
authors.lastname: Natarajan
authors.forename: Yogendra
authors.initials: Y
authors.lastname: Singh
authors.forename: Anand
authors.initials: A
authors.lastname: Ranganathan
mesh_terms: D000942:Antigens, Bacterial / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000737:chemistry; D020869:Gene Expression Profiling; D015723:Gene Library; D005822:Genetic Vectors; D006801:Humans; D008168:Lung / Q000382:microbiology*; D009169:Mycobacterium tuberculosis / Q000472:pathogenicity*; D010455:Peptides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry*; D040081:Protein Array Analysis; D011485:Protein Binding; D020798:Two-Hybrid System Techniques
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D018076:DNA, Complementary; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D010455:Peptides; D010649:Phenylalanine; D003576:Electron Transport Complex IV