PDBsum entry 3u1c

Contractile protein

PDB id: 3u1c

Contents

Protein chains

101 a.a.

Waters ×149

PDB id:

3u1c

Name:

Contractile protein

Title:

Anti-parallel dimer of n-terminal 98-aa fragment of smooth muscle tropomyosin alpha

Structure:

Tropomyosin alpha-1 chain. Chain: a, b. Fragment: unp residues 1-98. Engineered: yes

Source:

Gallus gallus. Bantam,chickens. Organism_taxid: 9031. Expressed in: escherichia coli. Expression_system_taxid: 469008.

Resolution:

1.80Å R-factor: 0.248 R-free: 0.284

Authors:

N.Jampani,R.Dominguez

Key ref:

J.N.Rao et al. (2012). Structural analysis of smooth muscle tropomyosin α and β isoforms. J Biol Chem, 287, 3165-3174. PubMed id: 22119916

Date:

29-Sep-11 Release date: 23-Nov-11

Protein chains

P04268  (TPM1_CHICK) -  Tropomyosin alpha-1 chain from Gallus gallus

Seq: 284 a.a.

Struc: 101 a.a.*

* PDB and UniProt seqs differ at 26 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.?

J Biol Chem 287:3165-3174 (2012)

PubMed id: 22119916

Structural analysis of smooth muscle tropomyosin α and β isoforms.

J.N.Rao, R.Rivera-Santiago, X.E.Li, W.Lehman, R.Dominguez.

ABSTRACT

A large number of tropomyosin (Tm) isoforms function as gatekeepers of the actin filament, controlling the spatiotemporal access of actin-binding proteins to specialized actin networks. Residues ∼40-80 vary significantly among Tm isoforms, but the impact of sequence variation on Tm structure and interactions with actin is poorly understood, because structural studies have focused on skeletal muscle Tmα. We describe structures of N-terminal fragments of smooth muscle Tmα and Tmβ (sm-Tmα and sm-Tmβ). The 2.0-Å structure of sm-Tmα81 (81-aa) resembles that of skeletal Tmα, displaying a similar super-helical twist matching the contours of the actin filament. The 1.8-Å structure of sm-Tmα98 (98-aa) unexpectedly reveals an antiparallel coiled coil, with the two chains staggered by only 4 amino acids and displaying hydrophobic core interactions similar to those of the parallel dimer. In contrast, the 2.5-Å structure of sm-Tmβ98, containing Gly-Ala-Ser at the N terminus to mimic acetylation, reveals a parallel coiled coil. None of the structures contains coiled-coil stabilizing elements, favoring the formation of head-to-tail overlap complexes in four of five crystallographically independent parallel dimers. These complexes show similarly arranged 4-helix bundles stabilized by hydrophobic interactions, but the extent of the overlap varies between sm-Tmβ98 and sm-Tmα81 from 2 to 3 helical turns. The formation of overlap complexes thus appears to be an intrinsic property of the Tm coiled coil, with the specific nature of hydrophobic contacts determining the extent of the overlap. Overall, the results suggest that sequence variation among Tm isoforms has a limited effect on actin binding but could determine its gatekeeper function.