PDBsum entry 1kql

Contractile protein

PDB id: 1kql

Contents

Protein chains

55 a.a. *

Waters ×27

* Residue conservation analysis

PDB id:

1kql

Name:

Contractile protein

Title:

Crystal structure of thE C-terminal region of striated muscle alpha- tropomyosin at 2.7 angstrom resolution

Structure:

Fusion protein of and striated muscle alpha-tropomyosin and the gcn4 leucine zipper. Chain: a, b. Engineered: yes. Other_details: n-terminal methionine followed by sequence database residues 255-278 of gcn4 leucine zipper and then c-terminal sequence database residues 254-284 of rat striated muscle alpha-tropomyosin

Source:

Saccharomyces cerevisiae, rattus norvegicus. Baker's yeast, norway rat. Organism_taxid: 4932, 10116. Strain: ,. Expressed in: escherichia coli. Expression_system_taxid: 562.

Biol. unit:

Tetramer (from PQS)

Resolution:

2.70Å R-factor: 0.252 R-free: 0.289

Authors:

Y.Li,S.Mui,J.H.Brown,J.Strand,L.Reshetnikova,L.S.Tobacman,C.Cohen

Key ref:

Y.Li et al. (2002). The crystal structure of the C-terminal fragment of striated-muscle alpha-tropomyosin reveals a key troponin T recognition site. Proc Natl Acad Sci U S A, 99, 7378-7383. PubMed id: 12032291 DOI: 10.1073/pnas.102179999

Date:

07-Jan-02 Release date: 29-May-02

Protein chains

P03069  (GCN4_YEAST) -  General control transcription factor GCN4 from Saccharomyces cerevisiae (strain ATCC 204508 / S288c)

Seq: 281 a.a.

Struc: 55 a.a.*

Protein chains

P04692  (TPM1_RAT) -  Tropomyosin alpha-1 chain from Rattus norvegicus

Seq: 284 a.a.

Struc: 55 a.a.*

* PDB and UniProt seqs differ at 22 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1073/pnas.102179999

Proc Natl Acad Sci U S A 99:7378-7383 (2002)

PubMed id: 12032291

The crystal structure of the C-terminal fragment of striated-muscle alpha-tropomyosin reveals a key troponin T recognition site.

Y.Li, S.Mui, J.H.Brown, J.Strand, L.Reshetnikova, L.S.Tobacman, C.Cohen.

ABSTRACT

Contraction in striated and cardiac muscles is regulated by the motions of a Ca(2+)-sensitive tropomyosin/troponin switch. In contrast, troponin is absent in other muscle types and in nonmuscle cells, and actomyosin regulation is myosin-linked. Here we report an unusual crystal structure at 2.7 A of the C-terminal 31 residues of rat striated-muscle alpha-tropomyosin (preceded by a fragment of the GCN4 leucine zipper). The C-terminal 22 residues (263-284) of the structure do not form a two-stranded alpha-helical coiled coil as does the rest of the molecule, but here the alpha-helices splay apart and are stabilized by the formation of a tail-to-tail dimer with a symmetry-related molecule. The site of splaying involves a small group of destabilizing core residues that is present only in striated muscle tropomyosin isoforms. These results reveal a specific recognition site for troponin T and clarify the physical basis for the unique regulatory mechanism of striated muscles.

Selected figure(s)

Figure 2.
Fig. 2. Structural basis for the splaying in the C-terminal region of striated muscle Tm. (A) In the C-terminal region of striated muscle -Tm, there are three consecutive "core" residues (blue) that are generally disfavored in two-stranded coiled coils: Gln-263 (d position), Tyr-267 (a position), and Ile-270 (d position). The two equivalent Ile side chains do not contact each other, and the pairs of Gln and Tyr side chains do not display the usual symmetric "knobs-into-holes" packing pattern. In each of these two cases (B and C), only one of the two equivalent residues is inserted into the hole on the opposite helix. Moreover, the distance between the two helices increases to accommodate the insertion of such long or bulky side chains.

Figure 3.
Fig. 3. Structural variations in the C-terminal region of different vertebrate Tm isoforms. (A) Coiled-coil predictions, using the program COILS (28-29) (with a 14-residue window size) for the C-terminal regions of the products of the -Tm gene. In striated-muscle -Tm, encoded by exon 9a (red squares), the coiled-coil propensity decreases sharply after Gln-263, consistent with a 22-residue splayed region observed in the current study (see Materials and Methods). Vertebrate smooth-muscle -Tm and many nonmuscle isoforms, encoded by exon 9d (green circles), are also predicted to be -helical but not in a two-stranded coiled-coil conformation at the C terminus. However, the coiled coil in these isoforms appears to extend beyond residue 262 to at least residue 270. In the brain isoforms, TmBr-1 and TmBr-3, encoded by exon 9c (dotted line), the C terminus is predicted to be an -helical coiled coil to the very end. In another brain isoform, TmBr-2, encoded by exon 9b (solid line), the C-terminal region is mostly likely not -helical because of three closely spaced prolines. (B) Schematic representation of the C-terminal ends of striated- and smooth-muscle -Tms.

Figures were selected by an automated process.