The three-dImensIonal structure of hevem, a low molecular weight protem Isolated from the latex of HCWI hru~r/~e~z~~s, has been determmed by X-ray dIffractIon at 2 8 A resolution The protein crystalhzes m space group P2,2,2,, with lattice constnnts u=21 78, h=31 86. c=Sl I2 A The structure was solvsd by molecular replacement methods usmg the domam C of wheat germ agglutmm (WGA) as search model The posmons and mdlvldual IsotropLc temperature factors of the 324 atoms have been refined by the HendrIckson and Konnert restrained refinement procedure Whde tight rcstrarnts have been mdmtdmed on the bonded dlstdnces and angles. the R-fdctor hds dropped to 24 1% and an averaged B value of 9 5 A2. usmg 78% (802) of the total possible number of rcflectlons m the resolution range 5-2 8 A The tertiary structure IS very snmlar to that of domam C of WGA from residues 3-31