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BIOGRAPHY:
Dr. Chitnis received his Ph.D. in biophysics from the University of California-Berkeley in 1990. He completed postdoctoral training in the Laboratory of Parasitic Diseases at the National Institutes of Health,
National Institute of Allergy and Infectious Disease. He received the
1995 ICAAC Young Investigator Award from the American Society of
Microbiology, the 1997 B.N. Singh Memorial Award from the Indian
Society of Parasitology, and the 2000 and 2001 M. O. T. Iyengar Awards
for Research in Malaria by the Indian Council of Medical Research. He
is currently a Research Scientist in the Malaria Group at the
International Centre for Genetic Engineering and Biotechnology in New
Delhi, India. His HHMI-funded work is on receptor-ligand interactions
involved in erythrocyte invasion by malaria parasites.
RESEARCH ABSTRACT SUMMARY:
The Central Role of Duffy Binding–Like (DBL) Domains in Interaction of Malaria Parasites with Host Receptors for Invasion and
Cytoadherence
Erythrocyte invasion by Plasmodium sp. merozoites and
cytoadherence of P. falciparum–infected erythrocytes to
host capillaries are two important pathogenic mechanisms in malaria. A
family of erythrocyte-binding proteins (EBPs), which includes P.
vivax and P. knowlesi Duffy-binding proteins (PvDBP and
PkDBP, respectively), mediates interaction with erythrocyte receptors
during invasion. Variant antigens (also known as PfEMP-1) expressed on
the surface of P. falciparum–infected erythrocytes bind to host
endothelial receptors to mediate cytoadherence.
We have used transfection technology to disrupt the gene encoding
PkDBP to study the protein's role in invasion. We demonstrate that the
interaction of PkDBP with Duffy antigen mediates junction formation, a
critical step during erythrocyte invasion. The receptor-binding
domains of EBPs and PfEMP-1 map to conserved cysteine-rich domains that
are referred to as Duffy binding–like (DBL) domains, after the first
receptor-binding domains identified from PvDBP and PkDBP. DBL domains
contain about 350 amino acids with 12–16 conserved cysteines.
Using chimeric constructs and mild proteolysis in conjunction with
functional binding assays, we provide evidence for a multidomain
architecture for DBL domains from EBPs and PfEMP-1. The N-terminal
region containing cysteines 1–4 of PvDBP and PkDBP forms a
distinct subdomain that is nonfunctional. The region containing
cysteines 5–12 of PvDBP and PkDBP forms another subdomain that is
capable of receptor binding. Expression of various deletion constructs
on the surface of COS cells followed by functional binding assays
demonstrates that receptor-binding sites of DBL domains derived from
EBPs and PfEMP-1 usually lie in the central region spanning the
equivalent of cysteines 5–8 of PvDBP and PkDBP. Site-directed
mutagenesis is being used to identify the receptor-binding residues
within this region. Understanding the structure-function relation of
the interaction of DBL domains with host receptors is key to the
development of receptor-blocking strategies that inhibit invasion or
reverse cytoadherence.
Photo: Kent Kallberg, Kallberg Studios
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