title: Identification and structural characterization of an unusual RING-like sequence within an extracellular biomineralization protein, AP7.
abstract: The RING or Really Interesting New Gene represents a family of eukaryotic sequences that bind Zn (II) ions and participate in intracellular processes involving protein-protein interaction. Although found in over 400 different proteins, very little is known regarding the structure-function properties of these domains because of the aggregation problems associated with RING sequences. To augment this data set, we report an unusual 36 AA C-terminal sequence of an extracellular matrix mollusk shell protein, AP7, that exhibits partial homology to the RING family. This Cys, His-containing sequence, termed AP7C, binds Zn (II) and other multivalent ions, but does not utilize a tetracoordinate complexation scheme for binding such as that found in Zn (II) finger polypeptides. Moreover, unlike Zn (II) finger and RING domains, this 36 AA can fold into a relatively stable structure in the absence of Zn (II). This folded structure consists of three short helical segments (A, B, and C), with segments A and B separated by a 4 AA type I beta-turn region and segments B and C separated by a 7 AA loop-like region. Interestingly, the putative RING-like region, -RRPFHECALCYSI-, experiences slow conformational exchange between two structural states in solution, most likely in response to imido ring interconversion at P8 and P21. Poisson-Boltzmann solvation calculations reveal that the AP7C molecular surface possesses a cationic region near its N-terminus, which lies adjacent to the 30 AA mineral modification domain in the AP7 protein. Given that the AP7C sequence does not influence mineralization, it is probable that this cationic pseudo-RING region is utilized by the AP7 protein for other tasks such as protein-protein interaction within the mollusk shell matrix.
authors.affiliation: Laboratory for Chemical Physics, Center for Biomolecular Materials Spectroscopy, New York University, 345 E. 24th Street, Room 1007, New York, New York 10010, USA.
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Collino
authors.forename: Il Won
authors.initials: IW
authors.lastname: Kim
authors.forename: John Spencer
authors.initials: JS
authors.lastname: Evans
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002113:Calcification, Physiologic / Q000502:physiology*; D002942:Circular Dichroism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008974:Mollusca; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000378:metabolism; D016335:Zinc Fingers
chemical_list: D011506:Proteins; D015032:Zinc