Protein Folds
Back to Main Index . . . last updated 12th.April'95
To best appreciate the content of this chapter you need to INTERACTIVELY EXAMINE
a number of protein structures.
If you haven't done so already, we STRONGLY URGE you to install
the FREE molecular viewer software, RasMol and configure it to be automatically
invoked by chemical/MIME. See our Technology Page to find
out how.
Since the two well-defined secondary structural units of helices and sheets are
abundant in proteins, families of protein structures have been classified by
a system based upon the alpha-helix and beta sheet and their general topological
properties. Each different topology may be considered as a fold. Current
thinking suggests that there are a limited number of folds found in
naturally occuring proteins.:-
- All-Alpha folds, in which the secondary structure
is almost exclusively alpha-helical
- All-Beta folds, in which the secondary structure is
composed almost exclusively of beta-sheets
- Alpha/Beta folds, consisting of helices and sheets
arranged in beta-alpha-beta units, in which the beta-sheet strands are parallel
(refer to the chapter on Supersecondary
Structure )
- Alpha+Beta folds, in which the helices and sheets
tend to be spatially separated in different parts of the protein; there is a lack
of beta-alpha-beta supersecondary structure
- Small disulphide rich proteins which have few
helices or sheets; this kind of fold occurs in a number of protein modules (see
the section on mosaic proteins in the
previous chapter
- See also the note on Protein Structure
Terminology
- References
You are also advised to study these databases of structural classification
Remember, if you know the 4-letter PDB code, you MAY be able to access the structure
using a URL of the form http://www.cryst.bbk.ac.uk/PDB/pdbcode.pdb
If you have MAGE installed and configured for Chemical MIME, you can view the
Branden and Tooze,
Protein Science and
Protein Tourist Kinemages, some of which are relevant to this material.
Again, refer to the
Technology Page if necessary.
There are some links to appropriate Kinemages within this chapter.
Credits
We wish to thank the following for material incorporated into this chapter
John Overington, Birkbeck & Pfizer
Gail Schumann & Jane Richardson
Alexey G. Murzin, Steven E. Brenner, Tim J.P. Hubbard, and Cyrus Chothia for SCOP
C.A. Orengo, A.D. Michie, J.M. Thornton, & W.R. Taylor for CATH
Manuel Peitsch, GLAXO, Geneva
John Walshaw & Alan Mills, Birkbeck College, Apr'95