protein, associated with the membrane skeleton, which promotes the binding of spectrin to
actin in a calcium/calmodulin dependent manner. The
protein is composed of two similar sub-units, a-adducin (
103kd) and b-adducin (97kd)
which together form higher order structures (dimers & tetramers) (Matsuoka
et al, ). Each sub-unit is composed of two distinct
domains:- a globular, protease resistant head domain and a helical tail domain. The head domain contains a sequence which is
similar to the actin binding domain of the ABP-120, dystrophin, a-actinin
group. However as attempts to bind this domain to F-actin
have failed, the significance of this is uncertain. The tail domain contains the putative
calmodulin binding sites and the sites of phosphorylation by protein kinase A. Protein kinase C sites are thought to be close to
the junction of the head and tail domains.
A MARKS homologous domain is present at the C-terminus of adducin that is
thought to be responsible for actin binding. The
dimers are thought to bind head to head and tail to tail in an parallel fashion,
via the neck region which would be consistent with the reported bundling activity.
Adducin apparently recruits spectrin to the barbed ends of actin filaments
through the MARKS domain (Li
et al, 1998)
capping the filaments so that in the erythrocyte at least CapZ cannot bind the
& Fowler, 1997).
Although this protein was
first isolated from erythrocyte membrane it has since been found in other tissues such as
kidney, brain and liver and in Drosophila a homolog is required for ring
canal formation (Yue
& Spradling, 1992).
spontaneous hypertensive rat strain has been identified and revealed later to be
caused by a mutation in an adducin gene. It seems that adducin may be
connected to the disease as it has been found that adducin associates with the
et al, 1999).
M., Salardi, S., Tripodi, G., Barassi, P., Rivera, R., Manunta, P., Goldshleger,
R., Ferrari, P., Bianchi, G. & Karlish, S. J. (1999) Evidence for an
interaction between adducin and Na+-K+-ATPase: relation to
genetic hypertension., Am.J.Physiol. 277, H1338-H1349.
Kuhlman, P. A. and V.
M. Fowler (1997). "Purification and characterization of an a1b2
isoform of CapZ from human erythrocytes: Cytosolic location and inability to
bind to Mg2+ ghosts suggest that erythrocytes actin filaments are
capped by adducin." Biochemistry 36, 13461-13472.
Li, X., Y. Matsuoka, et
al. (1998). "Adducin prefferentially recruits spectrin to the fast growing
ends of actin filaments in a complex requiring the MARKS-related domain and a
newly defined oligomerization domain." J.Biol.Chem. 273(30),
Matsuoka, Y., X. Li, et
al. (2000). "Adducin: Structure, function and regulation." Cell and
Molecular Life Sciences 57, 884-895.
Yue, L., &
Spradling, A.C. (1992). "hu-li tai shao, a gene required for ring
canal formation during Drosophila oogenesis, encodes a homolog of adducin."
Genes Dev. 6, 2443-2454.