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Hemolin, a plasma protein from lepidopteran insects, is composed of four immunoglobulin domains. Its synthesis is induced by microbial challenge. We investigated the biological functions of hemolin inManduca sexta.It was found to bind to the surface of bacteria and yeast, and caused these micro-organisms to aggregate. Hemolin was demonstrated to bind to lipopolysaccharide (LPS) from Gram-negativebacteriaand to lipoteichoic acid fromGram-positive bacteria. | Eur. J. Biochem. 269 1827-1834 2002 FEBS 2002 doi 10.1046 j.1432-1033.2002.02830.x Binding of hemolin to bacterial lipopolysaccharide and lipoteichoic acid An immunoglobulin superfamily member from insects as a pattern-recognition receptor Xiao-Qiang Yu and Michael R. Kanost Department of Biochemistry Kansas State University Manhattan KS USA Hemolin a plasma protein from lepidopteran insects is composed of four immunoglobulin domains. Its synthesis is induced by microbial challenge. We investigated the biological functions of hemolin in Manduca sexta. It was found to bind to the surface of bacteria and yeast and caused these micro-organisms to aggregate. Hemolin was demonstrated to bind to lipopolysaccharide LPS from Gram-negative bacteria and to lipoteichoic acid from Grampositive bacteria. Binding of hemolin to smooth-type forms of LPS was competed for efficiently by lipoteichoic acid and by rough mutant Ra and Rc forms of LPS which differ in polysaccharide length. Binding of hemolin to LPS was partially inhibited by calcium and phosphate. Hemolin bound to the lipid A component of LPS and this binding was completely blocked by free phosphate. Our results suggest that hemolin has two binding sites for LPS one that interacts with the phosphate groups of lipid A and one that interacts with the O-specific antigen and the outer-core carbohydrates of LPS. The binding properties of M. sexta hemolin suggest that it functions as a pattern-recognition protein with broad specificity in the defense against microorganisms. Keywords hemolin insect immunity lipopolysaccharide lipoteichoic acid pattern recognition receptor. Upon microbial infection insects synthesize defensive plasma proteins which include antimicrobial peptides and proteins lectins and cell adhesion molecules 1-3 . One such protein is hemolin a member of the immunoglobulin Ig superfamily. Hemolin contains four Ig domains of the I-set type which are most similar to those in neural cell adhesion molecules 4-6 . .
