LENGTH VARIATION IN THE KERATAN SULFATE DOMAIN OF MAMMALIAN AGGRECAN

The keratan sulfate domain of aggrecan consists of a series of tandeml y repeating hexapeptides which have the consensus sequence Glu-Glu/Lys -Pro-Phe-Pro-Ser, where the serine side-chains presumably provide site s for the attachment of keratan sulfate (KS) chains. The number of hex apeptide repeats varies between species, ranging from four in rat (Doe ge et al., 1987) and mouse (Walcz et al., 1992) to 13 in human (Doege et al., 1991) and 23 in bovine aggrecan (Antonsson et al., 1989). Chic ken aggrecan (Chandrasekaran and Tanzer, 1992) does not contain a I(S domain with a recognizable hexapeptide motif. The extent of this varia tion among mammalian and avian species is not known, and there is curr ently no explanation to predict how differences in the size of the KS domain would affect aggrecan function. We used polymerase chain reacti on (PCR) to amplify the portion of the human, canine and porcine aggre can gene that codes for the KS domain. We sequenced the amplified prod ucts in each case. Human aggrecan, with 13 hexapeptide repeats (Doege et al., 1987), was used as reference and found to be essentially ident ical to published data. The canine and porcine KS domains consisted of six and ten hexapeptide repeats respectively. The same PCR protocol w as used to amplify the KS domain from genomic DNA of eight other mamma lian species. Comparison of the size of these amplified products, as d etermined by agarose gel electrophoresis, with those for which sequenc e data are available allowed us to estimate the number of repeats in t he KS domain. In almost half the species examined, the KS domain consi sted of 13 hexapeptide repeats.