Structural and functional analysis of PDI-related proteins

MACROMOLECULES C25016 of their cysteines.Although no clear evidence exists for a physiological function of mammalian CRISP found mainly in the epididymis and salivary glands, snake venom CRISP are known to inhibit smooth muscle contraction and cyclic nucleotide-gated (CNG) ion channels.The structure of CRISP-a from Naja atra is determined at 1.58-Å resolution using the sulfur-SAD method and consists of unique disulfide patterns and two distinct structural domains: a protease sandwich fold (N-terminal) and an ion channel-blocking BgK toxin fold (C-terminal).With one positively charged cluster found at water accessible helix regions next to the Ser-His-Glu triad of the protease domain, heparin binding plays a role in regulating CRISP-a activity.As important residues identified to block CNG and K + channels of other toxin homologues are located at one face of the ion channel-blocking domain, the structure provides a basis for rational design of a peptide blocker of the CNG channel.The ion channelblocking domain and heparin-binding site of CRISP-a are suggested to play a chaperone role in leading it to the site of protease action for remodeling of the extracellular matrix in mammalian cells.