V. PROGRAM IN STRUCTURAL BIOLOGY 
The Program in Structural Biology, initiated in 
1986, is the most recently established of the five 
HHMI research areas. Investigators in this program 
are located at The Johns Hopkins University, Har- 
vard College, the University of Texas Southwestern 
Medical Center at Dallas, Baylor College of Medi- 
cine, Yale University, Columbia University, and the 
University of California at San Francisco. These in- 
vestigators are examining the physical structure and 
organization of biologic materials through the tech- 
niques of x-ray crystallography, electron and optical 
imaging, nuclear magnetic resonance spectroscopy, 
and advanced computerized three-dimensional 
image reconstruction. The Institute is also support- 
ing the development of a nev^ beam line at the syn- 
chrotron at the Brookhaven National Laboratory, 
which will serve as a resource for the larger bio- 
medical community, as well as for investigators 
within HHMI. 
The research of Assistant Investigator Axel T. 
Briinger, Ph.D. (Yale University) and his colleagues 
is at the interface between theory and experiment 
in the area of structural biophysics. Their research 
tools are simulation methods of computational 
chemistry, adapted to the requirements of macro- 
molecular systems. Their current research effort 
centers on the development and applications of 
macromolecular structure determination and re- 
finement, based on x-ray crystallographic or nu- 
clear magnetic resonance (NMR) spectroscopic 
data. Structures of the influenza virus hemaggluti- 
nin with altered receptor binding complexed with 
cellular receptor analogues have been refined by 
simulated annealing, and a new search strategy 
based on Patterson correlation refinement has been 
developed to obtain initial phases for single-crystal 
diffraction data by molecular replacement. 
The work of Investigator Wayne A. Hendrickson, 
Ph.D. (Columbia University) and his colleagues fea- 
tures a mix of crystallographic methodology devel- 
opment and the applications of this technology to 
biologically significant problems. Of particular im- 
portance in the past year has been the further de- 
velopment of general methods for introducing ap- 
propriate anomalous scattering centers for direct 
structural analysis by the multiwavelength anoma- 
lous diffraction (MAD) method, using synchrotron 
radiation. Selenomethionyl proteins produced in 
recombinant systems and synthetic brominated 
nucleic acids serve well in this regard. These tech- 
niques have been used in the structural analysis of 
a bromoDNA/drug complex and of interleukin-la. 
MAD analyses on selenomethionyl thioredoxin and 
ribonuclease H are also well advanced. 
The laboratory of Associate Investigator David A. 
Agard, Ph.D. (University of California at San Fran- 
cisco) focuses on understanding the relationship 
between structure and function at the cellular and 
molecular levels. In a collaboration with the labora- 
tory of Investigator John W Sedat, Ph.D. (University 
of California at San Francisco), Dr. Agard is using 
novel three-dimensional imaging methods to inves- 
tigate the structure of mitotic chromosomes and to 
examine their spatial and temporal behavior through- 
out the mitotic cell cycle. At a molecular level, 
Dr. Agard's group is using a combination of site- 
directed mutagenesis, solution kinetics, and x-ray 
crystallography to probe the structural basis of en- 
zyme specificity, using the bacterial serine protease 
a-lytic protease as a model system. Biochemical, ge- 
netic, and structural approaches are being used to 
investigate the unusual folding pathway of a-lytic 
protease, since it provides a unique opportunity for 
studying a stable folding intermediate and the "fold- 
ase" that converts it to the mature, active enzyme. 
Determination of the crystal structure of apolipo- 
protein E (apoE), an important protein in human 
cholesterol metabolism, is also being pursued. 
Dr. Sedat's efforts are directed at reaching a 
structural understanding of the interphase chromo- 
somes in the eukaryotic nucleus through an ap- 
proach that is at the limits of optical and electron 
microscopic resolution for three-dimensional analy- 
sis. Drosophila is used as a genetically and develop- 
mentally defined model organism. Dr. Sedat's 
group has developed and applied real-time three- 
dimensional optical microscopy for living samples, 
three-dimensional structure analysis of the distribu- 
tion of the nuclear envelope protein lamin, and 
three-dimensional in situ hybridization of specific 
DNA probes. 
Investigator Johann Deisenhofer, Ph.D. (Univer- 
sity of Texas Southwestern Medical Center at Dal- 
las) and his colleagues have continued their work 
on aspects of the three-dimensional structure of a 
large pigment-protein complex, the photosynthetic 
reaction center from a purple bacterium. Sitting in 
the cell membrane of Rhodopseudomonas viridis, 
this molecule performs the first steps in photosyn- 
thesis, the conversion of light energy into chemical 
energy. Knowledge of this structure has already led 
to a better understanding of photosynthesis. 
Continued 
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