cated in the ball and yet-to-be-determined binding 
sites in the tail. The 440-kDa brain ankyrin is a novel 
structural protein with the potential to extend from 
the membrane into the cytoplasm and interact with 
cytoskeletal elements. 
In the future, Dr. Bennett and his colleagues will 
work to identify the protein (s) in unmyelinated 
axons that interacts with the 440-kDa ankyrin, par- 
ticularly the tail domain, and to elucidate the molec- 
ular mechanisms regulating transcription of this 
gene and alternative splicing of its pre-mRNA. 
Brain Ankyrin-binding Proteins Related 
to Neural Cell Adhesion Molecules 
A 1 86-kDa integral plasma membrane protein rep- 
resenting 0.3% of total rat brain membrane protein 
has been identified as an ankyrin-binding protein 
and found to be colocalized with ankyrin and coex- 
pressed with the adult form of ankyrin in postna- 
tal development. The sequences of this ankyrin- 
binding protein, deduced from cDNA clones, and 
two related polypeptides indicate that these pro- 
teins are closely related to neurofascin, a membrane- 
spanning neural cell adhesion molecule in the Ig 
superfamily previously implicated in axonal bun- 
dling in development of embryonic chicken brain. 
The predicted cytoplasmic domains of the rat 
ankyrin-binding protein and chicken neurofascin 
are nearly identical and closely related to a group of 
neural cell adhesion molecules with variable extra- 
cellular domains, which include LI, Nr-CAM, and 
Ng-CAM of vertebrates and neuroglian of Drosoph- 
ila. The ability of ankyrin to bind to neurofascin and 
possibly to the related cell adhesion molecules may 
be important in determining the localization of 
these proteins on the cell surface and in providing a 
mechanical linkage extending between cells and in- 
cluding cytoplasmic structural proteins. A physio- 
logical consequence of convergence of cytoskele- 
tal, transmembrane, and intercellular connections 
in adult brain may be stabilization of the structure of 
the nervous system so that this intricate arrangement 
of cells can survive the traumas of everyday life. 
Ankyrin Structure and Regulation 
The membrane-binding domains of ankyrins are 
composed of a tandem series of 3 3 -amino acid re- 
peats that are responsible for recognition of the an- 
ion exchanger as well as other targets for ankyrin. 
The 33-residue repeats are present in a variety of 
proteins with diverse functions, including regula- 
tion of transcription factors, cell cycle regulation, 
and even neurotoxicity in the case of a spider 
venom. Functions requiring macromolecular recog- 
nition are common functions that ankyrin and these 
proteins share. A solution to the structure of ankyrin 
repeats would therefore be useful both in terms of 
understanding ankyrin function and more generally. 
As a first step, the basic folding unit of ankyrin re- 
peats has been defined, with the unanticipated re- 
sult that six repeats are required for a stable globular 
structure. It should now be possible, in principle, to 
obtain crystals of the six-repeat unit, which has been 
expressed in bacteria, and to solve the atomic struc- 
ture by x-ray crystallography. 
An activated ankyrin identified in previous work 
is missing a l63-residue portion of its regulatory 
domains because of alternative splicing of pre- 
mRNA. Recent experiments support the idea that 
the alternatively spliced segment within the regula- 
tory domain of ankyrin performs a repressor func- 
tion and acts through an allosteric mechanism in- 
volving interaction (s) at a site separate from the 
binding site for the anion exchanger. These findings 
provide insight into functional consequences of 
alternate exon usage and mechanisms of ankyrin 
regulation. 
A grant from the National Institutes of Health sup- 
ported the project described above. 
Dr. Bennett is also Professor of Biochemistry at 
Duke University Medical Center. 
Articles 
Bennett, V. 1992. Ankyrins. Adaptors between di- 
verse membrane proteins and the cytoplasm. / 
Biol Chem 267:8703-8706. 
Bennett, V., Otto, E., Davis, D., Davis, L., and Kor- 
deli, E. 1991. Ankyrins: a family of proteins that 
link diverse membrane proteins to the spectrin 
skeleton. Curr Top Membr 38:65-77. 
Bennett, V., Otto, E., Kunimoto, M., Kordeli, E., 
and Lambert, S. 1991. Diversity of ankyrins in the 
brain. Biochem Soc Trans 19:1034-1039. 
Hu, R.-J., and Bennett, V. 1991. In vitro proteoly- 
sis of brain spectrin by calpain I inhibits associa- 
tion of spectrin with ankyrin-independent 
membrane binding site(s). / Biol Chem 266: 
18200-18205. 
Joshi, R., Gilligan, D.M., Otto, E., McLaughlin, T., 
and Bennett, V. 1991 • Primary structure and do- 
main organization of human alpha and beta addu- 
cin. f Cell Biol 115:665-675. 
Kordeli, E., and Bennett, V. 1991 . Distinct ankyrin 
isoforms at neuron cell bodies and nodes of Ran- 
vier resolved using erythrocyte ankyrin-deficient 
mice, f Cell Biol 114:1243-1259. 
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