Structural Studies of Hyperthermophilic Viruses

Structural Studies of Hyperthermophilic Viruses. Crenarchaeal viruses are very unique; they are usually found to exist in extreme thermal environments (greater than 70°C), and frequently at extreme pH (1.0 < pH < 4.0), conditions commonly encountered in the hot springs of Yellowstone.  Sulfolobus Spindle Virus 1 (SSV1) and Sulfolobus Turreted Icosahedral Virus (STIV) are arguably the best studied of these crenarchaeal viruses.  The genomes of both viruses have been sequenced, but the majority of the open reading frames have yet to be assigned any function.  We are engaged in structural and biochemical studies of the SSV and STIV proteomes in an effort to elucidate the functions of these proteins.
Due to lack of similarity with the public databases, sequence data alone has largely failed to unlock the functions of these viral genomes.  It is unlikely, however, that the majority of a genome is unique. It is well known that tertiary (3D) similarities between proteins persist far longer on the evolutionary time scale than either primary (amino acid) or genomic sequence (DNA) similarities.  Our work over the last three years clearly demonstrates the validity of this approach, tertiary structure does suggest function.  Importantly, the insights gained from our structural studies suggest function for an ever increasing number of viral proteins.  These structure-function relationships are relevant not only to the viruses under study (SSVs and STIV), but for the Crenarchaea in general.  Further, our work has also contributed to structural studies illustrating important evolutionary relationships among viruses in the three domains of life, and to an understanding of protein stability at extreme temperatures.

Structural Studies of the Response to Oxidative Stress in Archaea.  Oxidative stress, in which reactive oxygen species (ROS) react indiscriminately with DNA, proteins and lipids, is a universal phenomenon experienced by organisms in all domains of life.  Cumulative damage from ROS is now thought to contribute to numerous disease states.  Thus, an understanding of the molecular response to oxidative stress is of significant medical importance.
In collaboration with the Douglas and Young laboratories, we have initiated studies of the oxidative stress response in Sulfolobus solfataricus, a model Crenarchaeote.  Initial work has identified a DPS-like protein (SsDPSL) whose transcript levels are highly up regulated in response to hydrogen peroxide.  The structure of SsDPSL reveals a new class of proteins containing a “thioferritin” motif.  Current efforts are focused on elucidating the functional details of this motif, and studies on similar proteins in human pathogens.  In addition to our studies of the DPSL protein, microarray data has identified several other proteins that are strongly up regulated in response to oxidative stress.  We are beginning structural characterization of these proteins as well.

Fig. 1. Surface Residues on One Face of the ORF D-63 Dimer are Highly Conserved. Conserved positive, negative, and non-charged residues are colored blue, red, and grey respectively. Non-conserved residues are colored yellow. 180 degree rotation shows strong sequence conservation between SSV1, SSV2, and SSV RH along one face perpendicular to the 2-fold symmetry axis. Two smaller regions of conserved surface are found on the opposite side. ORFD-63 might serve as an adaptor molecule in the assembly of larger macromolecular complexes vital to viral propagation.

Fig. 2. The Structure of F-93 Reveals a Winged Helix DNA Binding Motif. The DNA has been docked here by superposition of the winged helix protein 1F4K and its accompanying DNA onto F-93, followed by deletion of the 1F4K protein. This leaves the 1F4K DNA docked to F-93, and suggests the manner in which F-93 might bind DNA. The structure suggests that F-93 is a transcription factor regulating expression of viral and/or host proteins.

Current Laboratory Personnel:

George Gauss, Postdoctoral Associate
Eric Larson, Ph.D. Student
Smita Menon, Ph.D. Student.
Annop Sendamarai, Ph.D. Student
Nathanael Lintner, Undergraduate Student
Björn Trankle, Undergraduate Student
Brian Eilers, Technical Support Staff

Return to regular view	Text-only	Updated: 12/11/08