title: Formation of metal nanoclusters on specific surface sites of protein molecules.
abstract: During vacuum condensation of metals on frozen proteins, nanoclusters are preferentially formed at specific surface sites (decoration). Understanding the nature of metal/protein interaction is of interest for structure analysis and is also important in the fields of biocompatibility and sensor development. Studies on the interaction between metal and distinct areas on the protein which enhance or impede the probability for cluster formation require information on the structural details of the protein's surface underlying the metal clusters. On three enzyme complexes, lumazine synthase from Bacillus subtilis, proteasome from Thermoplasma acidophilum and GTP cyclohydrolase I from Escherichia coli, the decoration sites as determined by electron microscopy (EM) were correlated with their atomic surface structures as obtained by X-ray crystallography. In all three cases, decoration of the same protein results in different cluster distributions for gold and silver. Gold decorates surface areas consisting of polar but uncharged residues and with rough relief whereas silver clusters are preferentially formed on top of protein pores outlined by charged and hydrophilic residues and filled with frozen buffer under the experimental conditions. A common quality of both metals is that they strictly avoid condensation on hydrophobic sites lacking polar and charged residues. The results open ways to analyse the binding mechanism of nanoclusters to small specific sites on the surface of hydrated biomacromolecules by non-microscopic, physical-chemical methods. Understanding the mechanism may lead to advanced decoration techniques resulting in fewer background clusters. This would improve the analysis of single molecules with regard to their symmetries and their orientation in the adsorbed state and in precrystalline assemblies as well as facilitate the detection of point defects in crystals caused by misorientation or by impurities.
authors.affiliation: Department of Chemistry, Technical University Munich, Lichtenbergstr. 4, Garching, Germany.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Braun
authors.forename: Winfried
authors.initials: W
authors.lastname: Meining
authors.forename: Ulrike
authors.initials: U
authors.lastname: Hars
authors.forename: Markus
authors.initials: M
authors.lastname: Fischer
authors.forename: Rudolf
authors.initials: R
authors.lastname: Ladenstein
authors.forename: Robert
authors.initials: R
authors.lastname: Huber
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Sevil
authors.initials: S
authors.lastname: Weinkauf
authors.forename: Luis
authors.initials: L
authors.lastname: Bachmann
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology; D001665:Binding Sites; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D006136:GTP Cyclohydrolase / Q000737:chemistry* / Q000378:metabolism*; D006046:Gold / Q000378:metabolism; D008670:Metals / Q000378:metabolism*; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism*; D010165:Palladium / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D012258:Riboflavin Synthase / Q000737:chemistry / Q000378:metabolism; D012834:Silver / Q000378:metabolism; D013822:Thermoplasma / Q000201:enzymology
chemical_list: D029968:Escherichia coli Proteins; D008670:Metals; D009097:Multienzyme Complexes; D012834:Silver; D010165:Palladium; D006046:Gold; C044822:6,7-dimethyl-8-ribityllumazine synthase; D012258:Riboflavin Synthase; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D006136:GTP Cyclohydrolase