Biology Reference
In-Depth Information
2.
S
PINOPHILIN
S
TRUCTURE
The rat and human spinophilin proteins consist of 817 amino acids and shares 96%
sequence identity [Allen et al., 1997; Vivo et al., 2001]. The protein contains one F-actin-, a
receptor- and a PP1c- binding domains, a PDZ and three coiled-coil domains. Figure 1
provides a schematic diagram of the main neurabins structural domains.
Figure 1. A schematic representation of the domain structure of full-length spinophilin (A) and neurabin
1 (B)
Spinophilin has been isolated from rat brain as a protein interacting with F-actin [Satoh et
al., 1998]. Its F-actin-binding domain determined to be amino acids 1-154 is both necessary
and sufficient to mediate actin polymers binding and cross-linking. Nuclear Magnetic
Resonance (NMR) and circular dichroism (CD) spectroscopy studies showed that spinophilin
F-actin-binding domain is intrinsically unstructured and that upon binding to F-actin it adopts
a more ordered structure (a phenomenom also called folding-upon-binding). Another actin
binding property, namely a F-actin pointed end capping activity was recently proposed for
this domain [Schüler and Peti, 2007]. Spinophilin, PP1c and F-actin can form a trimeric
complex in vitro.
A receptor-interacting domain, located between amino acids 151-444,
interacts with the
third intracellular loop (3i) of various seven transmembrane domain receptors [Smith et al.,
1999; Richman et al., 2001] such as D2 dopamine and some subtypes of α-adrenergic
receptors.
The primary PP1c-binding domain is located within residues 417-494 of spinophilin and
this domain contains a pentapeptide motif (R/K-R/K-V/I-X-F) between amino acids 447 and
451 that is conserved in other PP1c regulatory subunits. This canonical PP1c-binding domain
binds to the hydrophobic groove in the catalytic subunit. It was suggested that the canonical
motif anchors PP1c to its binding proteins and facilitates diverse arrays of secondary
interactions that play a role in modulating the overall strength of the interactions, regulating
