Structural Correlates of Protein Function

Marianne Schiffer
Senior Biophysicist

Bldg: 202. Room: A 145

E-mail: mschiffer@anl.gov

Phone: (630) 252-3883
Fax: (630) 252-3387

 

Curriculum Vitae
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I. Structure and function of heme proteins important in bioremediation

Geobacter sulfurreducens is a bacterium useful in bioremediation. Our research has been focused on two families of cytochromes and sensor domains of chemotaxis/signal transduction proteins from this organism. This work is part of collaboration with Prof. Derek R. Lovley (UMass) GTL project.  Individual heme reduction potential determinations and ligand binding studies were performed in the laboratory of Dr. Carlos A. Salgueiro (Universidade Nova de Lisboa, Portugal).

(1) The three-heme cytochrome c7 family – G. sulfurreducens encodes five small (~10 kDa) cytochromes each containing three c-type hemes. We have expressed and isolated the c7 molecules from E. coli, and their structures were determined by X-ray crystallography. The c7 family cytochromes have been implicated in metal reduction processes of G. sulfurreducens. The structure of one of the cytochromes, PpcA, is shown. PpcA is one of the most abundant cytochromes in the periplasm of G. sulfurreducens and it can reduce metal ions in vitro. Relevant Publications Family of cytochrome c7-type proteins from Geobacter sulfurreducens: structure of one cytochrome c7 at 1.45 A resolution. Production and preliminary characterization of a recombinant triheme cytochrome c(7) from Geobacter sulfurreducens in Escherichia coli.

(2) Novel cytochromes containing c7-type domains – G. sulfurreducens encodes three novel cytochromes (two with 12-hemes and one with 27-hemes) with sequences that can be divided into domains of homology to cytochrome c7 family. We have determined the structure of one of the domains from GSU1996. Relevant Publications Heterologous expression of dodecaheme "nanowire" cytochromes c from Geobacter sulfurreducens. Heterologous expression of hexaheme fragments of a multidomain cytochrome from Geobacter sulfurreducens representing a novel class of cytochromes c. Structure of a novel c7-type three-heme cytochrome domain from a multidomain cytochrome c polymer.

 

(3) Sensor domains of chemotaxis proteins – G. sulfurreducens encodes many signal transduction proteins. We identified two groups of periplasmic c-type heme containing sensor domains that are part of transmembrane chemotaxis/signal transduction proteins. We have determined the structures of two of these sensor domains from chemotaxis proteins (GSU0582 and GSU0935). These structures revealed a novel PAS domain formed by swapping of two protein chains.

Relevant Publications

• Structures and solution properties of two novel periplasmic sensor domains with c-type heme from chemotaxis proteins of Geobacter sulfurreducens: implications for signal transduction.
• Characterization of a c-type heme-containing PAS sensor domain from Geobacter sulfurreducens representing a novel family of periplasmic sensors in Geobacteraceae and other bacteria.

II. Hydrolytic enzymes We have crystallized catalytic domains of three hydrolytic enzymes important in biofuels research in collaboration with scientists from USDA, Peoria, IL. We have recently determined the structure of the catalytic domain of glucuronoyl esterase (Cip2) from Hypocrea jecorina (formerly known as Trichoderma reesei). This is the first structure of the recently established carbohydrate esterase family 15 (http://www.cazy.org/fam/CE15.html).

Relevant Publications

• Crystallization and preliminary X-ray diffraction analysis of the glucuronoyl esterase catalytic domain from Hypocrea jecorina.

III. Stabilization of immunoglobulin domains

Structural determinants of stability in immunoglobulin light chain variable domain are explored in collaboration with Drs. Fred J. Stevens and R. Wilton.

Relevant Publications

• Factors contributing to decreased protein stability when aspartic acid residues are in beta-sheet regions.
• Increasing protein stability by polar surface residues: domain-wide consequences of interactions within a loop.

IV. Proton transfer in transmembrane proteins

Structural studies of photosynthetic reaction center (RC) mutants that influence proton transfer. We have determined structures of RCs carrying additional mutations that restore proton transfer function to inactive L212Glu → Ala, L213Asp → Ala double mutant and L212Glu → Gln mutant RCs are studied. Our data suggests that additional mutations could influence the RC structure up to 40 Å distance from the mutation site. (In collaborations with Drs. D.K. Hanson and P.D. Laible)

Relevant Publications

• Temperature and cryoprotectant influence secondary quinone binding position in bacterial reaction centers.
• The structure of a mutant photosynthetic reaction center shows unexpected changes in main chain orientations and quinone position.