Herpes simplex virus type I and 2 (HSV-1 and -2) glycoproteins D (gD-1 and gD-2) play a role in the entry of the virus into the host cell. Availability of substantial amounts of these proteins, or large fragments thereof. will he needed to allow studies at the molecular level. We studied the potency of the Pichia pastoris yeast expression system to produce Soluble forms of gD. The DNA sequences encoding the extracellular domains of gD {amino acids 1-314 (gD-1((1-314))) and amino acids 1 254 (gD-1((1-254))) of gD-1 and amino acids 1-314 of gD-2 (gD-2((1-314)))} were cloned into the P. pastoris yeast expression vector pPIC9, Two truncated forms of gD-1 were fitted with a His tail (designated as gD-1((1-314His)) and gD-1((1-254His))) to facilitate their purification. Large amounts of gD-1((1-314)) and gD-1((1-314His)) (280-300 mg/L induction medium) were produced, The yields of recombinant gD-1((1-254)) and gD-1((1-254His)) were lower: 20-36 mg/L. and the yield of the gD-2((1-314)) fragment was much lower: 6 mg/L. SDS PAGE analysis revealed multiple glycosylated species of the larger gD fragments, ranging in apparent molecular weight from 31 to 78 kDa. The smaller gD-1((1-254)) fragment appeared as two bands with molecular weights of 33 and 31 kDa. All recombinant proteins produced by P. pastoris were recognized, as expected, by a panel of MAbs (A16, DL6. A18. DL11, HD1, ABD1. and AP7). In addition, we showed that gD-1((1-314)), gD-2((1-314)), and gD-1((1-254His)) were able to interfere with binding of HSV to susceptible cells. These results indicate that the conformations of the recombinant proteins closely resemble those of native gD. (C) 2002 Elsevier Science (USA). All rights reserved.