Purification and characterization of two storage proteins from Locusta migratoria showing distinct developmental and hormonal regulation

Abstract

Two major hemolymph proteins, belonging to the insect hexameric storage protein family, have been purified from Locusta migratoria. Larval storage protein 1 (LSP1) has M r = 410,000, s = 16.1 S, 10% hexose content and is composed of up to five different 75 kDa subunits. Isoelectric focusing of native LSP1 shows a pI of about pH 6.0 with some microheterogeneity. Persistent storage protein (PSP) has a M r = 460,000, s = 16.4 S, 7% hexose and contains major 74 kDa and minor 77 kDa subunits. Native PSP has a pI of pH 5.6 also with some microheterogeneity. PSP dissociates reversibly into monomers at alkaline pH. The N-terminal sequence was determined for the PSP 74 kDa subunit. A previously identified cyanoprotein (CP), with M r = 435,000 and subunits of 69 kDa, was also purified. A second larval-specific storage protein, LSP2, has been identified but not purified. LSP1 and PSP exhibit distinct developmental patterns and hormonal regulation. LSP1 is larval-specific, increasing to a high concentration in the late fifth instar and disappearing in the early adult. PSP, however, remains abundant through the last larval instar and persists at a lower concentration in the adult. In fifth instar larvae, treatment with the juvenile hormone (JH) analog, pyriproxyfen, totally repressed production of LSP1, and significantly lowered the hemolymph level of PSP. In contrast, JH analog treatment is found to elevate the level of PSP in adults. Storage proteins which persist in the adult stage, under hormonal regulation that is switched during metamorphosis, may be characteristic of some hemimetabolous insects.