The 30K family of proteins is important in energy metabolism and may play a role in inhibiting cellular apoptosis in silkworms (Bombyx mori). Several 30K-family proteins have been identified. In this study, two new silkworm genes, referred to as Slp (NM 001126256) and Lsp-t (NM 001043443), were analyzed by a bioinformatics approach according to the sequences of 30K proteins previously reported in the silkworm. Both Slp and Lsp-t shared more than 41% amino acid sequence homology with the reported 30K proteins and displayed a conserved domain consistent with that of lipoprotein-11. Additionally, the cDNA sequences of both Slp and Lsp-t were obtained from the fat bodies of silkworm larvae by reverse transcription polymerase chain reaction. Both genes were expressed in BmN cells using the Bac-to-Bac system. Purified Slp and Lsp-t were added to cultured BmN and human umbilical vein endothelial cells (HUVEC) that were treated with H2O2. Both Slp and Lsp-t significantly enhanced the viability and suppressed DNA fragmentation in H2O2 treated BmN and HUVEC cells. This study suggested that Slp and Lsp-t exhibit similar biological activities as their known 30K-protein counterparts and mediate an inhibitory effect against H2O2-induced apoptosis. 1. Introduction The 30K-family proteins are lipoproteins synthesized by the fat body in the silkworm and display a molecular weight of approximately 30kD [1–3]. They are highly expressed in silkworm larvae during the early stage of the fifth instar and during the pupation stage of development, where they are predominantly located in the hemolymph as a major source of energy for growth, development, and pupation. In addition, the 30K-family proteins found in the silkworm are highly conserved, share more than 41% amino acid sequence homology, and display similar tertiary structures with the common conserved domain of lipoprotein-11 [4]. Moreover, the 30K family of proteins was found to have an antifungal activity [5]. Ujita et al. found that the purified recombinant glutathione-fused 30K protein Lp6G1 inhibited the morbidity of silkworm pupae and prolonged the life of the fungus-infected silkworm chrysalis [5]. Thus far, several 30K proteins were also reported to have an antiapoptotic activity [6–11]. Park et al. demonstrated that the purified 30Kc6 protein that was expressed in Escherichia coli, enhanced cell viability, and inhibited apoptosis of both virus-infected Sf9 cells and chemical-treated HeLa cells [6]. Rhee et al. discovered that the purified Escherichia coli expressed 30Kc19 protein enhanced cell viability and
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