Two antiapoptotic types of genes, iap and p35, were found in baculoviruses. P35 is a 35-kDa protein that can suppress apoptosis induced by virus infection or by diverse stimuli in vertebrates or invertebrates. iap homologues were identified in insects and mammals. Recently, we have identified sl-p49, a novel apoptosis suppressor gene and the first homologue of p35, in the genome of the Spodoptera littoralis nucleopolyhedrovirus. Here we show that sl-p49 encodes a 49-kDa protein, confirmed its primary structure that displays 48.8% identity to P35, and performed computer-assisted modeling of P49 based on the structure of P35. We demonstrated that P49 is able to inhibit insect and human effector caspases, which requires P49 cleavage at Asp94. Finally we identified domains important for P49's antiapoptotic function that include a reactive site loop (RSL) protruding from a B-barrel domain. RSL begins at an amphipathic a1 helix, traverses the a-sheet central region, exposing Asp94 at the apex, and rejoins the a-barrel. Our model predicted seven a-helical motifs, three of them unique to P49. a-Helical motifs a1, a2, and a4a were required for P49 function. The high structural homology between P49 and P35 suggests that these molecules bear a scaffold common to baculovirus "apoptotic suppressor" proteins. P49 may serve as a novel tool to analyze the contribution of different components of the caspase chain in the apoptotic response in organisms not related

In attempting to produce the HAP, endoplasmic reticulum (ER) targeted apoptosis-inducing protein, as a GSTfusion protein we found that the expression of HAP, but not GST alone, induced bacterial cell death. The HAP protein inhibited the bacterial growth within 30min after inducting HAP expression. The transmission electron microscopic examination revealed that the morphology of the bacterial cells expressing hap was changed dramatically: unusually elongated phenotype compared with those of controls and finally leading to cell death. The lethality of HAP was relieved by the addition of vitamin E as a reducing agent and under anaerobic growth conditions. These results suggest that a trace amount of HAP induces bacterial cell death and the death is related with reactive oxygen species (ROS).

asy gene is a novel apoptosis-inducing gene, but its mechanism is unclear. To investigate the mechanism of asy inducing apoptosis, a novel gene encoding ASY interacting protein (asyip) is isolated from human lung cell line (WI-38) cDNA library with yeast two-hybrid system. The asyip gene is constitutively expressed as two mRNA transcripts with the size of 1.8 and 2.7kb in various human tissues at different levels. Sequence analysis of full-length cDNA reveals that the two alternative transcripts of asyip gene contain common 5' end and different 3' end, and share a common open reading frame encoding a polypeptide of 236 amino acids. Two protein kinase C phosphorylation sites and two casein kinase II phosphorylation sites are found in ASYIP amino acid sequence. Two highly hydrophobic regions encoding potentially two transmembrane domains are present. The ASYIP protein contains a C-terminal endoplasmic reticulum retrieval signal (Lys-Lys-Lys-Ala-Glu). Immunoprecipitation assay confirmed the interaction of ASY and ASYIP in mammalian cells. Compared with asy gene, overexpression of asyip gene can inhibit growth of tumor cell Saos2 and induce cell apoptosis with a low efficiency.

A novel cloned Spodoptera littoralis Nucleopolyhedrovirus (SlNPV) p49 gene is able to suppress apoptosis of insect cells Sf9 triggered by virus. The amino acid sequence of P49 expressed in baculovirus expression system is the same as predicted, indicating that the expression of P49 is correct. Metabolic labeling revealed that p49 was able to be expressed both in the early and late phases after the viral infection, and only in the late phase was the expression driven by polyhedra promoter, but the amount of expression was higher than that of wtSlNPV. In summary, the early gene of SlNPV p49 as well as p35 of AcMNPV is able to be expressed in the late phase, but its promoter is weaker compared with polyhedra promoter. In vitro, P49 can be cut by Bm caspase and human caspase-3, yielding 10 and 40 ku fragments. Purified P49 blocks the substrate cleavage by Bm caspase and human caspase-3, showing that P49 inhibits downstream caspases in the apoptotic pathway.

Apoptosis, a wide physiological process in multicellular organisms, is critical for the organ development, the cell senescence, the tissue homeostasis and the resistance to infection of virus and bacteria. Apoptosis plays a key role in the regulation of the growth cell number such as the tissue construction, the elimination of abnormal or dangerous cells. Therefore, apoptosis is a stringent and effective cell quality controlling system, which reduces the number of harmful cells to the maximum, such as auto-immunity cell, cells infected by virus, tumor cells by cell suicide[1]. Apoptosis can be initiated by a wide variety of the extracellular and intracellular stimuli, including the developmental signals, the cellular stress and the disruption of cell cycle, transduced and amplified by the second messengers, and finally finished by the activating death effector protease. This process can be called apoptosis signal network. The defective in control of the apoptotic pathways may contribute to a variety of diseases including cancer, autoimmune and neurodegenerative conditions [2,3].