Insect Biochemistry and Molecular Biology 33 (2003) 389–395 www.elsevier.com/locate/ibmb The Musca domestica larval hexamerin is composed of multiple, similar polypeptides C.K. Moreira a1 , M. de L. Capurro a , E. Calvo ab , P.I. Silva jr. c , A.A. James b , A.G. deBianchi a , O. Marinotti ab,* a Departamento de Parasitologia, Instituto de Cie ˆncias Biome ´dicas, Universidade de Sa ˜o Paulo, Sa ˜o Paulo, SP 05508-900, Brazil b Department of Biochemistry and Molecular Biology, University of California Irvine, Irvine, CA 92697-3900, USA c Laborato ´rio de Artro ´podes, Instituto Butantan, Sa ˜o Paulo, SP05503-900, Brazil Received 30 August 2002; received in revised form 8 November 2002; accepted 27 November 2002 Abstract The Musca domestica larval hexamerin (MdHex-L) is a hexameric glycoprotein with an apparent native molecular weight of 500 kDa. Seven different cDNAs that encode MdHex-L subunits were cloned and sequenced. Furthermore, amino acid sequences of isolated subunits were determined by the Edman degradation method and compared to the conceptual translation products derived from the cloned cDNAs. The obtained data indicate the existence of multiple forms of MdHex-L subunits and that these multiple forms may be grouped into three categories according to their percentages of nucleotide sequence identity.  2003 Elsevier Science Ltd. All rights reserved. Keywords: Musca domestica; Hexamerin; Storage protein; Housefly 1. Introduction Hexamerins, abundant proteins found in the hemo- lymph of holometabolous insects, are high molecular weight molecules (~500,000 Da) composed of six hom- ologous or heterologous subunits with an average M r = 80,000 Da. These proteins are synthesized and secreted into the hemolymph by the fat body cells during the lar- val feeding stage. Later in development at the pre-pupal or beginning of pupal stages, hexamerins are selectively endocytosed and accumulated by the same fat body cells. During metamorphosis, hexamerins are hydrolyzed, and either are not detected, or are detected at low levels in adult insects. All holometabolous insect species analyzed so far synthesize one or more larval hexamerins. (Haunerland, 1996; Telfer and Kunkel, 1991). The main biological role for the larval hexamerins appears to be to supply amino acids for the synthesis of * Corresponding author. Tel.: +1-949-824-5930; fax: 1+949-824- 2814. E-mail address: omarinot@uci.edu (O. Marinotti). 1 Present address: Department of Genetics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4955, USA. 0965-1748/03/$ - see front matter  2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0965-1748(02)00256-4 adult tissues during metamorphosis, and also to provide energy for this process (Levenbook, 1985; Levenbook and Bauer, 1984; Pan and Telfer, 1999; Scheller, 1983; Telfer and Kunkel, 1991). As secondary functions, hex- amerins may provide energy for the maintenance of metabolism, carry hydrophobic substances such as lipids and ecdysteroids (Kanost et al., 1990), and participate as structural components of the cuticle (Marinotti et al., 1988; Peter and Scheller, 1991; Scheller et al., 1980). The common housefly, Musca domestica, is an insect of medical and veterinary importance worldwide. It is the most familiar nuisance pest and can cause human and animal myiasis. Moreover its biology and ecology makes it an ideal mechanical vector of human and ani- mal pathogens including viruses, bacteria, protozoan cysts and helminth eggs (Graczyk et al., 2001; Sukonta- son et al., 2000). During the last years our laboratory has studied several of the M. domestica hemolymph pro- teins and their involvement in insect development and reproduction. One of them, the M. domestica larval hex- amerin (MdHex-L) was described first by de Bianchi et al. (1983). The purified molecule was found to be a hex- americ glycoprotein with an apparent native molecular weight of 500 kDa, composed of two types of subunits