Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

Ra-KLP, a 75 amino acid protein secreted by the salivary gland of the brown ear tick Rhipicephalus appendiculatus has a sequence resembling those of Kunitz/BPTI proteins. We report the detection, purification and characterization of the function of Ra-KLP. In addition, determination of the three-dimensional crystal structure of Ra-KLP at 1.6 A resolution using sulphur single-wavelength anomalous dispersion reveals that much of the loop structure of classical Kunitz domains, including the protruding protease-binding loop, has been replaced by beta-strands. Even more unusually, the N-terminal portion of the polypeptide chain is pinned to the "Kunitz head" by two disulphide bridges not found in classical Kunitz/BPTI proteins. The disulphide bond pattern has been further altered by the loss of the bridge that normally stabilizes the protease-binding loop. Consistent with the conversion of this loop into a beta-strand, Ra-KLP shows no significant anti-protease activity; however, it activates maxiK channels in an in vitro system, suggesting a potential mechanism for regulating host blood supply during feeding.

Original publication

DOI

10.1016/j.jmb.2009.04.045

Type

Journal article

Journal

Journal of molecular biology

Publication Date

06/2009

Volume

389

Pages

734 - 747

Addresses

CEH Oxford, Mansfield Road, Oxford OX1 3SR, UK. gcp@ceh.ac.uk

Keywords

Cell Line, Saliva, Animals, Humans, Rhipicephalus, Aprotinin, Ion Channels, Crystallography, X-Ray, Patch-Clamp Techniques, Sequence Alignment, Evolution, Molecular, Phylogeny, Amino Acid Sequence, Protein Structure, Secondary, Protein Structure, Tertiary, Sequence Homology, Amino Acid, Dimerization, Models, Molecular, Molecular Sequence Data