Analysis of genetic heterogeneity in the HCAR adenovirus-binding Ig1 domain in a Caucasian Flemish population

Using two primersets in the adjacent intron sequences, HCAR exons 2 and 3, which comprise the full-length Ig1 domain, were amplified by polymerase chain reactions in 108 unselected and unrelated healthy Belgian volunteers. After nucleotide sequencing, no polymorphisms could be demonstrated in the adenovirus-binding Ig1 exons 2 and 3 of the HCAR gene.The adenovirus-binding Ig1 domain seems to be a highly conserved region in the Caucasian population which is a reassuring finding regarding adenovector-based gene therapy.Recombinant human subgroup C adenoviruses (serotypes 2 and 5) are envisaged as efficient vector delivery systems in gene therapy because of their ability to transfect a wide variety of cells [1]. Successful gene delivery requires viral entry into the target cell via specific receptor-mediated uptake [2]. For adenoviruses from subgroups A, C, D, E and F, the human coxsackie-adenovirus receptor (HCAR) protein functions as the primary high-affinity binding site for the knob domains of the adenoviral fibers, elongating from the viral capsid structure. Subsequent interactions between the viral penton base and cell surface αvβ3 and αvβ5 integrins induce virus internalization into the target cells [3].The gene that encodes HCAR is located on chromosome 21q11.2 and consists of seven exons that are distributed over an area of 54 kb [4]. After translation a 365-amino acid (aa) integral membrane glycoprotein is produced, with an N-terminal exoplasmic domain (218 aa), a single hydrophobic transmembrane-spanning region (21 aa) and a highly conserved cytoplasmic tail (107 aa) [5]. The extracellular portion of the receptor consists of two immunoglobulin-like domains: the N-terminal Ig1 is related to the immunoglobulin V fold and the more C-terminal Ig2 is related to the IgC2 fold. Structural analysis of the mechanism of adenovirus binding to HCAR revealed that only the Ig1 domain (exons 2 and 3) makes contact with the fiber knob. In contrast, molecular interactions of