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, compo sed of an N-terminal cysteine-rich domain, a fibronectin-like type II domain, and eight carbohydrate recognition domains (CRDs). It is thoug ht 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 mu tagenesis that OS1, a snake venom sPLA(2), binds to the receptor via i ts 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 a ble 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. T he M-type sPLA(2) receptor and the macrophage mannose receptor are hom ologous and are predicted to share the same tertiary structure. p-Amin ophenyl-alpha-D-mannopyranoside bovine serum albumin, a known ligand o f the macrophage mannose receptor, binds to the M-type sPLA(2) recepto r essentially via CRDs 3-6.