Our first attempt was to crystallize a baculovirus expressed human type II TGF-b receptor in complex with TGF-b1. Due to extensive glycosylation on the receptor, the crystallization trials with this receptor did not yield to any crystals. Subsequent deglycosylation procedure yielded a partially deglycosylated receptor which produced small crystals when complexed with TGF-b1.However, these crystals diffract poorly in the X-ray beam and not suitable for structure determination. To overcome the carbohydrate heterogeneity and low expression yield of the baculovirus expression system, we have cloned the soluble type II receptor gene into a bacteria expression vector. Due to a large number of disulfide bonds (12 cystines) present in this receptor, previous attempts by several groups to reconstitute the receptor have all failed. Our preliminary expression data suggests that approximately 20% of the protein is expressed in a non-aggregated soluble form and the rest is expressed in an inclusion body form using the bacteria system. The soluble part is shown to posses TGF-b binding by ELISA assays. After in vitro reconstitution, the refolded receptor from the inclusion body material is also active in the ELISA assay. We are refining the type II receptor bacteria expression system to obtain large quantity of receptor protein for crystallographic studies.
