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A new type of antimicrobial protein with multiple histidines from the hard tick, Amblyomma hebraeum
Author(s) -
Lai Ren,
Takeuchi Hajime,
Lomas Lee O.,
Jonczy Jan,
Rigden Daniel J.,
Rees Huw H.,
Turner Philip C.
Publication year - 2004
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.03-1154fje
Subject(s) - histidine , peptide sequence , biochemistry , hemolymph , recombinant dna , amino acid , biology , antimicrobial peptides , escherichia coli , microbiology and biotechnology , cysteine , antimicrobial , chemistry , peptide , enzyme , gene
A novel 11 kDa antimicrobial protein, named as hebraein, and having a unique amino acid sequence, was purified from the hemolymph of fed female Amblyomma hebraeum ticks. A full‐length cDNA clone encoding hebraein was isolated from a cDNA library made from tick synganglia. Hebraein consists of 102 amino acids, including 6 cysteine residues; has 9 histidines in its C‐terminal domain that are mainly present as HX repeats; and has no significant similarity to any known protein. The secondary structure prediction is very clearly all α‐helical (4–6 helices) except for a very short extension at the C terminus. Such high α‐helical content is quite different from known antimicrobial proteins. Recombinant hebraein and a mutant lacking the histidine residues in the C‐terminal domain were constructed and expressed. Assayed at the slightly acidic pH equivalent of fed female tick hemolymph, the wild‐type and the histidine‐rich recombinant hebraein had stronger antimicrobial activities than the histidine‐deficient mutant. The pH‐dependent properties of histidine‐rich antimicrobial proteins may allow the design of agents that would function selectively in specific pH environments. The results from protein profiling of hemolymph, analyzed by surface‐enhanced laser desorption/ionization time‐of‐flight (SELDI‐TOF) mass spectrometry combined with ProteinChip technology and RT‐PCR analysis suggested that this antimicrobial protein was up‐regulated by blood feeding. Our findings describe a new type of antimicrobial protein with multiple cysteine and histidine residues, and with unique secondary structure.