IDENTIFICATION OF THE BINDING DOMAIN FOR SECRETORY PHOSPHOLIPASES A(2) ON THEIR M-TYPE 180-KDA MEMBRANE-RECEPTOR

The rabbit muscle (M)-type receptor for secretory phospholipases A(2) (sPLA(2)s) has a large extracellular domain of 1394 amino acids, composed of an N-terminal cysteine-rich domain, a fibronectin-like type II domain, and eight carbohydrate recognition domains (CRDs). It is thought to mediate some of the physiological effects of mammalian sPLA(2)s, including vascular smooth muscle contraction and cell proliferation, and is able to internalize sPLA(2)s. Here, we show by site directed mutagenesis that OS1, a snake venom sPLA(2), binds to the receptor via its CRDs and that deletion of CRD 5 completely abolishes the binding of sPLA(2)s. Moreover, a receptor lacking all CRDs but CRD 5 was still able to bind OS1 although with a lower affinity. Deletion of CRDs 4 and 6, surrounding the CRD 5, slightly reduced the affinity for OS1, thus suggesting that these CRDs are also involved in the binding of OS1. The M-type sPLA(2) receptor and the macrophage mannose receptor are homologous and are predicted to share the same tertiary structure. p-Aminophenyl-alpha-D-mannopyranoside bovine serum albumin, a known ligand of the macrophage mannose receptor, binds to the M-type sPLA(2) receptor essentially via CRDs 3-6.