A NEW-TYPE OF HIGHLY POLYMERIZED YOLK PROTEIN FROM THE COCHINEAL INSECT DACTYLOPIUS-CONFUSUS

A female specific protein was isolated from eggs and female hemolymph of cochineal insects, using density gradient ultracentrifugation, ammo nium sulfate precipitation, and size exclusion column chromatography. The protein was found to consist of four different subunits with appar ent molecular weights (Mr) 45,000, 49,000, 53,000, and 56,000, respect ively. All four subunits were found to be glycosylated; no association of lipids was detected. Size exclusion column chromatography and non- denaturing polyacrylamide gel electrophoresis demonstrated that the na tive yolk protein exists as large polymers. Electron microscopy showed that these molecules are long, helical ribbons of variable size which are found in both hemolymph and eggs. Using cryo-electron microscopy, it was shown that the ribbons were 14.6 +/- 1.5 nm wide; the helix th ey form has a repeat distance of 104.9 +/- 11.3 nm and a diameter of 4 2.1 +/- 5 nm. A clear substructure of the ribbons was recognized. The newly identified protein is the major yolk protein of Dactylopius conf usus and no other proteins resembling the more familiar vitellins of o ther insect species were detected. Moreover, the D. confusus yolk prot ein appears to be unique both in its subunit structure and in its poly merizing qualities. Thus, the cochineal yolk protein (CYP) is suggeste d to represent a new type of insect yolk protein. (C) 1996 Wiley-Liss, Inc.