- The BBXB motif of RANTES is the principal site for heparin binding and controls receptor selectivity. Proudfoot, A.E., Fritchley, S., Borlat, F., Shaw, J.P., Vilbois, F., Zwahlen, C., Trkola, A., Marchant, D., Clapham, P.R., Wells, T.N. J. Biol. Chem. (2001)