A new type of antimicrobial protein with multiple histidines from the hard tick, Amblyomma hebraeum.
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 alpha-helical (4-6 helices) except for a very short extension at the C terminus. Such high alpha-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.
Lai
Ren
R
Cellular Regulation and Signaling Division, School of Biological Sciences, University of Liverpool, Liverpool, UK.
Takeuchi
Hajime
H
Lomas
Lee O
LO
Jonczy
Jan
J
Rigden
Daniel J
DJ
Rees
Huw H
HH
Turner
Philip C
PC
D000595:Amino Acid Sequence; D000818:Animals; D000890:Anti-Infective Agents / Q000737:chemistry* / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000235:genetics* / Q000494:pharmacology; D060829:Arthropod Proteins; D001769:Blood; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004435:Eating / Q000502:physiology; D005260:Female; D005786:Gene Expression Regulation; D015723:Gene Library; D006458:Hemolymph / Q000737:chemistry; D006639:Histidine / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D040081:Protein Array Analysis; D017433:Protein Structure, Secondary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013987:Ticks / Q000737:chemistry* / Q000235:genetics / Q000502:physiology
D000890:Anti-Infective Agents; D023181:Antimicrobial Cationic Peptides; D060829:Arthropod Proteins; D018076:DNA, Complementary; D012333:RNA, Messenger; C498557:hebraein protein, Amblyomma hebraeum; D006639:Histidine