The broad objective of our program has been the identification and characterization of polypeptides which may have immunological and physiological importance for the establishment and survival of malaria parasites in their hosts. The knobs mediate the sequestration of mature stages of Plasmodium falciparum in the host and sequestration is thought to offer some survival advantage to these parasites. The only identified constituent of the knobs is a histidine-rich protein, KP. The purpose of this study is to define the mechanisms involved in the biosynthesis and export of KP to the host erythrocyte membrane and to elucidate the chemical and genetic relationship of KP to an apparently related histidine-rich protein (HRP) of Plasmodium lophurae. To achieve these aims: (1) Pulse-chase studies will be carried out to determine whether, similar to other secretory proteins, KP is synthesized as a precursor polypeptide in vivo. (2) An in vitro cell-free system will be established to study the mechanisms involved in the synthesis and processing of KP. (3) A cDNA library will be constructed using mRNA from P. falciparum. Bacterial clones containing cDNA sequences of KP will be identified by exploiting the chemical analogies of KP and HRP and a variety of alternate approaches. (4) Identified cDNA clones will be characterized by sequencing and compared to sequences of cDNA of HRP. If long stretches of common sequences are identified, other species of malaria parasites will be examined for related histidine-rich protein genes.
