title: Implications on zinc binding to S100A2.
abstract: Human S100A2 is an EF-hand calcium-binding S100 protein that is localized mainly in the nucleus and functions as tumor suppressor. In addition to Ca2+ S100A2 binds Zn2+ with a high affinity. Studies have been carried out to investigate whether Zn2+ acts as a regulatory ion for S100A2, as in the case of Ca2+. Using the method of competition with the Zn2+ chelator 4-(2-pyridylazo)-resorcinol, an apparent Kd of 25 nM has been determined for Zn2+ binding to S100A2. The affinity lies close to the range of intracellular free Zn2+ concentrations, suggesting that S100A2 is able to bind Zn2+ in the nucleus. Two Zn2+-binding sites have been identified using site directed mutagenesis and several spectroscopic techniques with Cd2+ and Co2+ as probes. In site 1 Zn2+ is bound by Cys21 and most likely by His 17. The binding of Zn2+ in site 2 induces the formation of a tetramer, whereby the Zn(2+) is coordinated by Cys2 from each subunit. Remarkably, only binding of Zn2+ to site 2 substantially weakens the affinity of S100A2 for Ca2+. Analysis of the individual Ca2+-binding constants revealed that the Ca2+ affinity of one EF-hand is decreased about 3-fold, whereas the other EF-hand exhibits a 300-fold decrease in affinity. These findings imply that S100A2 is regulated by both Zn2+ and Ca2+, and suggest that Zn2+ might deactivate S100A2 by inhibiting response to intracellular Ca2+ signals.
authors.affiliation: Department of Biology, University of Konstanz, Universitätsstrasse 10, Postfach M665, 78457 Konstanz, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Koch
authors.forename: Shibani
authors.initials: S
authors.lastname: Bhattacharya
authors.forename: Torsten
authors.initials: T
authors.lastname: Kehl
authors.forename: Mario
authors.initials: M
authors.lastname: Gimona
authors.forename: Milan
authors.initials: M
authors.lastname: Vasák
authors.forename: Walter
authors.initials: W
authors.lastname: Chazin
authors.forename: Claus W
authors.initials: CW
authors.lastname: Heizmann
authors.forename: Peter M H
authors.initials: PM
authors.lastname: Kroneck
authors.forename: Günter
authors.initials: G
authors.lastname: Fritz
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002630:Chemotactic Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D003035:Cobalt / Q000737:chemistry / Q000378:metabolism; D014644:Genetic Variation / Q000235:genetics; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D009418:S100 Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism; D015032:Zinc / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002630:Chemotactic Factors; D008024:Ligands; D009418:S100 Proteins; C098997:S100A2 protein, human; D003035:Cobalt; D014443:Tyrosine; D015032:Zinc; D002118:Calcium