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Invariant Ser211 is involved in the catalysis of PD‐L4, type I RIP from Phytolacca dioica leaves
Author(s) -
Chambery Angela,
Pisante Marianna,
Di Maro Antimo,
Di Zazzo Erika,
Ruvo Menotti,
Costantini Susan,
Colonna Giovanni,
Parente Augusto
Publication year - 2007
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.21271
Subject(s) - polynucleotide , tryptophan , ribosome , biochemistry , residue (chemistry) , stereochemistry , dna , ribosome inactivating protein , site directed mutagenesis , chemistry , active site , biology , mutant , enzyme , rna , amino acid , gene
Multiple sequence alignment analysis of ribosome inactivating proteins (RIPs) has revealed the occurrence of an invariant seryl residue in proximity of the catalytic tryptophan. The involvement of this seryl residue in the catalytic mechanism of RIPs was investigated by site‐directed mutagenesis in PD‐L4, type 1 RIP isolated from Phytolacca dioica leaves. We show that the replacement of Ser211 with Ala apparently does not influence the N ‐β‐glycosidase activity on ribosomes (determined as IC 50 in a cell‐free system), but it reduces the adenine polynucleotide glycosylase activity (APG), assayed spectrophotometrically on other substrates such as DNA, rRNA, and poly(A). The ability of PD‐L4 to deadenylate polynucleotides appears more sensitive to the Ser211Ala replacement when poly(A) is used as substrate, as only 33% activity is retained by the mutant, while with more complex and heterogeneous substrates such as DNA and rRNA, its APG activity is 73% and 66%, respectively. While the mutated protein shows a conserved secondary structure by CD, it also exhibits a remarkably enhanced tryptophan fluorescence. This indicates that, although the overall protein tridimensional structure is maintained, removal of the hydroxyl group locally affects the environment of a Trp residue. Modelling and docking analyses confirm the interaction between Ser211 and Trp207, which is located within the active site, thus affecting RIP adenine polynucleotide glycosylase activity. Data accumulated so far confirm the potential involvement of Ser211 in the catalytic mechanism of type 1 RIP PD‐L4 and a possible role in stabilizing the conformation of Trp207 side chain, which participates actively in the protein enzymatic activity. Proteins 2007. © 2007 Wiley‐Liss, Inc.