A beta helix is a
tandem protein repeat structure formed by the association of parallel
beta strands in a helical pattern with either two or three
faces. The beta helix is a type of
solenoid protein domain. The structure is stabilized by inter-strand
hydrogen bond
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
s,
protein-protein interactions, and sometimes bound metal
ions. Both left- and right-handed beta helices have been identified. These structures are distinct from
jelly-roll folds, a different protein structure sometimes known as a "double-stranded beta helix".
The first beta-helix was observed in the enzyme
pectate lyase
Pectate lyase () is an enzyme involved in the maceration and soft rotting of plant tissue. Pectate lyase is responsible for the eliminative cleavage of pectate, yielding oligosaccharides with 4-deoxy-α-D-mann-4-enuronosyl groups at their non-re ...
, which contains a seven-turn helix that reaches 34 Å (3.4
nm) long. The
P22 phage
''Salmonella virus P22'' is a bacteriophage in the ''Podoviridae'' family that infects '' Salmonella typhimurium''. Like many phages, it has been used in molecular biology to induce mutations in cultured bacteria and to introduce foreign gen ...
tail spike protein, a component of the P22
bacteriophage
A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bac ...
, has 13 turns and in its assembled homo
trimer is 200 Å (20 nm) in length. Its interior is close-packed with no central pore and contains both hydrophobic residues and charged residues neutralized by
salt bridges.
Both pectate lyase and
P22 tailspike protein contain right-handed helices; left-handed versions have been observed in
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s such as
UDP-N-acetylglucosamine acyltransferase and archaeal
carbonic anhydrase
The carbonic anhydrases (or carbonate dehydratases) () form a family of enzymes that catalyze the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions). The active sit ...
.
Other proteins that contain beta helices include the
antifreeze
An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...
proteins from the beetle ''
Tenebrio molitor'' (right-handed)
and from the
spruce budworm
''Choristoneura'' is a genus of moths in the family Tortricidae. Several species are serious pests of conifers, such as spruce and are known as spruce budworms.
Species
*'' Choristoneura adumbratanus'' (Walsingham, 1900)
*'' Choristoneura afri ...
, ''
Choristoneura fumiferana
''Choristoneura fumiferana'', the eastern spruce budworm, is a species of moth of the family Tortricidae native to the eastern United States and Canada. The caterpillars feed on the needles of spruce and fir trees. Eastern spruce budworm po ...
'' (left-handed),
where regularly spaced
threonine
Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), a carboxyl group (which is in the deprotonated −COO� ...
s on the β-helices bind to the surface of
ice crystals and inhibit their growth.
Beta helices can associate with each other effectively, either face-to-face (mating the faces of their triangular prisms) or end-to-end (forming hydrogen bonds). Hence, β-helices can be used as "tags" to induce other proteins to associate, similar to
coiled coil
A coiled coil is a structural motif in proteins in which 2–7
alpha-helices are coiled together like the strands of a rope. (Dimers and trimers are the most common types.) Many coiled coil-type proteins are involved in important biological fu ...
segments.
Members of the
pentapeptide repeat family have been shown to possess a quadrilateral beta-helix structure.
References
External links
SCOP family of right-handed β-helicesCATH β-helix protein family
{{Spirals
Protein folds
Helices