Pierisins and CARP-1: ADP-ribosylation of DNA by ARTCs in butterflies and shellfish.

Abstract

The cabbage butterfly, Pieris rapae, and related species possess a previously unknown ADP-ribosylating toxin, guanine specific ADP-ribosyltransferase. This enzyme toxin, known as pierisin, consists of enzymatic N-terminal domain and receptor-binding C-terminal domain, or typical AB-toxin structure. Pierisin efficiently transfers an ADP-ribosyl moiety to the N(2) position of the guanine base of dsDNA. Receptors for pierisin are suggested to be the neutral glycosphingolipids, globotriaosylceramide (Gb3), and globotetraosylceramide (Gb4). This DNA-modifying toxin exhibits strong cytotoxicity and induces apoptosis in various human cell lines, which can be blocked by Bcl-2. Pierisin also produces detrimental effects on the eggs and larvae of the non-habitual parasitoids. In contrast, a natural parasitoid of the cabbage butterfly, Cotesia glomerata, was resistant to this toxin. The physiological role of pierisin in the butterfly is suggested to be a defense factor against parasitization by wasps. Other type of DNA ADP-ribosyltransferase is present in certain kinds of edible clams. For example, the CARP-1 protein found in Meretrix lamarckii consists of an enzymatic domain without a possible receptor-binding domain. Pierisin and CARP-1 are almost fully non-homologous at the amino acid sequence level, but other ADP-ribosyltransferases homologous to pierisin are present in different biological species such as eubacterium Streptomyces. Possible diverse physiological roles of the DNA ADP-ribosyltransferases are discussed.