Articles 
Haran, T.E., Joachimiak, A., and Sigler, P.B. 1992. 
The DNA target of the trp repressor. EMBO J 
11:3021-3030. 
Joachimiak, A., and Sigler, P.B. 1991. Crystalliza- 
tion of protein-DNA complexes. Methods Enzy- 
mol 208:82-99. 
Myatt, E.A., Stevens, F.J., and Sigler, P.B. 1991. Ef- 
fects of pH and calcium ion on self-association 
properties of two dimeric phospholipases A2. / 
Biol Chem 266:16331-16335. 
Pathak, D., and Sigler, P.B. 1992. Updating struc- 
ture-function relationships in the bZip family of 
transcription factors. Curr Opin Struct Biol 
2:116-123. 
Scott, D.L., Achari, A., Christensen, P.A., Viljoen, 
C.C., and Sigler, P.B. 1991- Crystallization and 
preliminary diffraction analysis of caudoxin and 
notexin; two monomeric phospholipase A2 neuro- 
toxins. Toxicon 29:1517-1521. 
Scott, D.L., White, S R., Browning, J.L., Rosa, J.J., 
Gelb, M.H., and Sigler, P.B. 1991. Structures of 
free and inhibited human secretory phospholi- 
pase A2 from inflammatory exudate. Science 
254:1007-1010. 
STRUCTURAL STUDIES OF REGULATORY AND SIGNAL-TRANSDUCTION PROTEINS 
Stephen R. Sprang, Ph.D., Associate Investigator 
Three-Dimensional Structures of the TNF 
Cytokine Family and Their Receptors 
Dr. Sprang's laboratory continues its structural 
studies of members of the tumor necrosis factor 
(TNF) family of cytokine hormones, which includes 
TNF-a, synthesized by macrophages, and lympho- 
toxin (TNF-jS), a product of lymphocytes. The cells 
of individual tissues respond differently to TNF-a 
and lymphotoxin, depending on their developmen- 
tal lineage and tissue-specific functions. Systemic 
manifestations include the induction of the inflam- 
matory response, shock, and cachexia. Both cyto- 
kines are directly toxic to certain tumor cell lines. 
Lymphotoxin is 32% identical to TNF-a in primary 
sequence and binds to the same receptors. 
The laboratory has determined the structures of 
both TNF-a and TNF-;S (research completed by Dr. 
Michael Eck). The determination of the crystal 
structure of TNF-/3 to a resolution of 1.9 A, with 
crystals provided by Drs. Mark Ultsch, Abraham 
DeVos, and Anthony A. Kossiakoflf (Genentech), was 
reported this year. Lymphotoxin is topologically 
identical to TNF-a, although the structures differ 
near sites of length variation. Both molecules assem- 
ble as trimers, stabilized primarily by hydrophobic 
amino acids, but the trimer interface of lympho- 
toxin is notably rich in aromatic residues. The struc- 
ture of TNF-j8 is currently being refined with high- 
resolution data to allow a comparative analysis of 
trimer stabilization in TNF-a and TNF-;8. 
Dr. Sprang's laboratory continues its structural 
studies of the TNF receptor. Several laboratories 
have cloned two distinct receptors, both of which 
are capable of engaging TNF-a and lymphotoxin. 
Collaborating with Drs. Barbara Brandhuber and Ta- 
dahiko Khono (Synergen) , the Sprang laboratory has 
produced crystals of the extracellular domain of the 
so-called 55-kDa TNF receptor. These crystals be- 
long to the orthorhombic space group P2j2i2i (a 
= 77.6 A, ft = 85.1 A, c = 68.2 A). These crystals 
diffract to ~ 2. 8 A. A second, possibly monoclinic 
crystal form has also been obtained. Several possible 
heavy-atom derivatives of the orthorhombic crystals 
have been identified by Dr. Lynn Rodseth, and data 
sets for these have been measured. 
The extracellular domain of the 55-kDa TNF re- 
ceptor is the first member of this family to have been 
crystallized. Work is now in progress to crystallize 
the complexes between TNF-a or lymphotoxin and 
either receptor's extracellular domain. The labora- 
tory has isolated stable complexes between TNF-a 
and the extracellular domain of the 55-kDa receptor 
by high-performance liquid chromatography (HPLC) . 
Structure of Basic Fibroblast Growth Factor 
Last year the laboratory reported the 1 .8-A resolu- 
tion structure of basic fibroblast growth factor 
(bFGF), a polypeptide of 146 residues with mito- 
genic activity. The factor stimulates the prolifera- 
tion of many cell types, including fibroblasts, endo- 
thelial cells, and myoblasts. The molecule contains 
a heparin-binding site that anchors it to glycoamino- 
glycan components of the extracellular matrix and 
promotes interaction of the factor with its receptor. 
The structure reveals that FGF belongs to the same 
structural family as interleukins-la and 
Crystals have now been obtained of a complex 
between bFGF and a small oligosaccharide analogue 
STRUCTURAL BIOLOGY 487 
