title: The structure of hookworm platelet inhibitor (HPI), a CAP superfamily member from Ancylostoma caninum.
abstract: Secreted protein components of hookworm species include a number of representatives of the cysteine-rich/antigen 5/pathogenesis-related 1 (CAP) protein family known as Ancylostoma-secreted proteins (ASPs). Some of these have been considered as candidate antigens for the development of vaccines against hookworms. The functions of most CAP superfamily members are poorly understood, but one form, the hookworm platelet inhibitor (HPI), has been isolated as a putative antagonist of the platelet integrins αIIbβ3 and α2β1. Here, the crystal structure of HPI is described and its structural features are examined in relation to its possible function. The HPI structure is similar to those of other ASPs and shows incomplete conservation of the sequence motifs CAP1 and CAP2 that are considered to be diagnostic of CAP superfamily members. The asymmetric unit of the HPI crystal contains a dimer with an extensive interaction interface, but chromatographic measurements indicate that it is primarily monomeric in solution. In the dimeric structure, the putative active-site cleft areas from both monomers are united into a single negatively charged depression. A potential Lys-Gly-Asp disintegrin-like motif was identified in the sequence of HPI, but is not positioned at the apex of a tight turn, making it unlikely that it interacts with the integrin. Recombinant HPI produced in Escherichia coli was found not to inhibit the adhesion of human platelets to collagen or fibrinogen, despite having a native structure as shown by X-ray diffraction. This result corroborates previous analyses of recombinant HPI and suggests that it might require post-translational modification or have a different biological function.
authors.affiliation: Laboratory of Malaria and Vector Research, NIH/NIAID, 12735 Twinbrook Parkway, Rockville, MD 20852, USA.
authors.forename: Dongying
authors.initials: D
authors.lastname: Ma
authors.affiliation: Laboratory of Malaria and Vector Research, NIH/NIAID, 12735 Twinbrook Parkway, Rockville, MD 20852, USA.
authors.forename: Ivo M B
authors.initials: IM
authors.lastname: Francischetti
authors.affiliation: Laboratory of Malaria and Vector Research, NIH/NIAID, 12735 Twinbrook Parkway, Rockville, MD 20852, USA.
authors.forename: Jose M C
authors.initials: JM
authors.lastname: Ribeiro
authors.affiliation: Laboratory of Malaria and Vector Research, NIH/NIAID, 12735 Twinbrook Parkway, Rockville, MD 20852, USA.
authors.forename: John F
authors.initials: JF
authors.lastname: Andersen
mesh_terms: D020816:Amino Acid Motifs; D000722:Ancylostoma / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000737:chemistry / Q000187:drug effects*; D020134:Catalytic Domain; D002448:Cell Adhesion / Q000187:drug effects*; D003094:Collagen / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005340:Fibrinogen / Q000737:chemistry / Q000378:metabolism; D015870:Gene Expression; D015801:Helminth Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006860:Hydrogen Bonding; D038982:Integrin alpha2beta1 / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000378:metabolism; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: C476807:HPI-1 protein, Ancylostoma caninum; D015801:Helminth Proteins; D038982:Integrin alpha2beta1; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011994:Recombinant Proteins; D005340:Fibrinogen; D003094:Collagen
keywords: antigen V; hemostasis; parasitism