Long loops in proteins.
In proteins, loop regions which connect secondary structures are generally short (80% are <10 amino acids long). However, long loops, defined here as > or = 10 residues, do occur. Two types of long loop may be distinguished: those which connect adjacent regions of secondary structure ('long-closed') and those which connect distant secondary structures ('long-open'). Only 5% of all loops in proteins fall into the long-open class. Inspection of these unusual long-open loops reveals a higher percentage of proline residues and more helix-helix linkages than expected. Exposure to solvent is similar for long-open and long-closed loops. The role of these loops in protein folding is discussed.
Martin
A C
AC
Department of Biochemistry and Molecular Biology, University College London, UK.
Toda
K
K
Stirk
H J
HJ
Thornton
J M
JM
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