title: Proline 235 plays a key role in the regulation of the oligomeric states of Thermotoga maritima Arginine Binding Protein.
abstract: The Arginine Binding Protein isolated from Thermotoga maritima (TmArgBP) is a protein endowed with several peculiar properties. We have previously shown that TmArgBP dimerization is a consequence of the swapping of the C-terminal helix. Here we explored the structural determinants of TmArgBP domain swapping and oligomerization. In particular, we report a mutational analysis of the residue Pro235, which is located in the hinge region of the swapping dimer. This residue was either replaced with a Gly-Lys dipeptide (TmArgBP(P235GK)) or a Gly residue (TmArgBP(P235G)). Different forms of these mutants were generated and extensively characterized using biophysical techniques. For both TmArgBP(P235GK) and TmArgBP(P235G) mutants, the occurrence of multiple oligomerization states (monomers, dimers and trimers) was detected. The formation of well-folded monomeric forms for these mutants indicates that the dimerization through C-terminal domain swapping observed in wild-type TmArgBP is driven by conformational restraints imposed by the presence of Pro235 in the hinge region. Molecular dynamics studies corroborate this observation by showing that Gly235 assumes conformational states forbidden for Pro residues in the TmArgBP(P235G) monomer. Unexpectedly, the trimeric forms present: (a) peculiar circular dichroism spectra, (b) a great susceptibility to heating, and (c) the ability to bind the Thioflavin T dye. The present findings clearly demonstrate that single-point mutations have an important impact on the TmArgBP oligomerization process. In a wider context, they also indicate that proteins endowed with an intrinsic propensity to swap have an easy access to states with altered structural and, possibly, functional properties.
authors.affiliation: IRCCS SDN, Via Emanuele Gianturco, 113, 80143 Napoli, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Smaldone
authors.affiliation: Department of Sciences and Technologies, Università del Sannio, Via Port'arsa 11, Benevento 82100, Italy.
authors.forename: Marilisa
authors.initials: M
authors.lastname: Vigorita
authors.affiliation: Institute of Biostructures and Bioimaging, CNR, Via Mezzocannone 16, I-80134 Napoli, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Ruggiero
authors.affiliation: Institute of Biostructures and Bioimaging, CNR, Via Mezzocannone 16, I-80134 Napoli, Italy; DiSTABiF, Second University of Naples, Caserta 81100, Italy.
authors.forename: Nicole
authors.initials: N
authors.lastname: Balasco
authors.affiliation: Department of Chemistry, University of Richmond, Richmond, VA 23173, USA.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Dattelbaum
authors.affiliation: Institute of Food Science, CNR, Via Roma, 64, Avellino, Italy.
authors.forename: Sabato
authors.initials: S
authors.lastname: D'Auria
authors.affiliation: Department of Chemical Sciences, University of Naples Federico II, Via Cintia, 80126 Napoli, Italy.
authors.forename: Pompea
authors.initials: P
authors.lastname: Del Vecchio
authors.affiliation: Department of Sciences and Technologies, Università del Sannio, Via Port'arsa 11, Benevento 82100, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Graziano
authors.affiliation: Institute of Biostructures and Bioimaging, CNR, Via Mezzocannone 16, I-80134 Napoli, Italy. Electronic address: luigi.vitagliano@unina.it.
authors.forename: Luigi
authors.initials: L
authors.lastname: Vitagliano
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000378:metabolism*; D002152:Calorimetry, Differential Scanning; D002352:Carrier Proteins / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D011392:Proline; D055503:Protein Multimerization; D055550:Protein Stability; D020124:Thermotoga maritima / Q000737:chemistry*
chemical_list: D002352:Carrier Proteins; D001120:Arginine; D011392:Proline
keywords: Differential scanning calorimetry; Domain swapping; Protein oligomerization; Protein structure dynamics; Protein structure-stability