Complete amino-acid sequence of PD-S2, a new ribosome-inactivating protein from seeds of Phytolacca dioica L.
The primary structure has been determined for PD-S2, a new type 1 ribosome-inactivating protein (RIP), isolated from the seeds of Phytolacca dioica L. PD-S2 has 265 amino-acid residues, and a molecular mass of 29586 Da. The polypeptide chain contains four amino-acid residues more than PAP-S, a type-I RIP isolated from the seeds of the taxonomically related plant Phytolacca americana L. We have compared the amino-acid sequence of PD-S2 with those of two other RIPs with known three-dimensional structure: PAP-S and ricin A-chain (RTA), the active chain of the best known type-2 RIP. This analysis shows an identity of 76% and 33% with PAP-S and RTA respectively, and a similarity of 82% and 54%. Comparison with the PAP sequence, isolated from leaves of P. americana, shows an even higher identity (80%) and similarity (87%). Furthermore, the amino-acid residues reported in other RIPs to be invariant and participate in the definition of the active site (Tyr-76, Tyr-127, Glu-179, Arg-182 and Trp-211; PD-S2 numbering) are all present. Asn-74, Arg-138, Gln-175, and Glu-208 are also conserved, while Asn-209 is substituted by Glu, all residues located in the active-site cleft of RIPs (Tahirov, T.H., Lu, T.-H., Liaw, Y.-C., Chen, J.L. and Lin, J.Y. (1995) Crystal structure of abrin-a at 2.14 A, J. Mol. Biol. 250, 354-367). The polypeptide chain of PD-S2 contains two N-glycosylation sites at Asn-112 and Asn-120, the second of which appears to be linked to sugars. Like PAP-S, PD-S2 does not contain free sulfhydryl groups. The four cysteinyl residues of the two proteins have corresponding sequence positions, most likely with identical S-S pairing.
Del Vecchio Blanco
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F
Dipartimento di Chimica Organica e Biologica, Università di Napoli Federico II, Italy.
Bolognesi
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A
Malorni
A
A
Sande
M J
MJ
Savino
G
G
Parente
A
A
D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D003488:Cyanogen Bromide; D008969:Molecular Sequence Data; D009699:N-Glycosyl Hydrolases / Q000737:chemistry* / Q000302:isolation & purification; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D037121:Plant Lectins; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification; D011487:Protein Conformation; D054789:Ribosome Inactivating Proteins, Type 1; D012270:Ribosomes; D012276:Ricin / Q000737:chemistry; D012639:Seeds / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012984:Software
D010446:Peptide Fragments; D037121:Plant Lectins; D010940:Plant Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D012276:Ricin; D009699:N-Glycosyl Hydrolases; C105087:PD-S2 protein, Phytolacca dioica; C024275:pokeweed antiviral protein; D003488:Cyanogen Bromide