PDBsum entry 1nug

Transferase

PDB id: 1nug

Contents

Protein chain

675 a.a. *

Metals

_MG ×2

_CL ×4

_CA ×4

Waters ×809

* Residue conservation analysis

PDB id:

1nug

Name:

Transferase

Title:

Role of calcium ions in the activation and activity of the transglutaminase 3 enzyme (2 calciums, 1 mg, inactive form)

Structure:

Protein-glutamine glutamyltransferase e. Chain: a, b. Synonym: tgase e, tge, tge, transglutaminase 3. Engineered: yes. Mutation: yes

Source:

Homo sapiens. Human. Organism_taxid: 9606. Gene: tgm3. Expressed in: spodoptera frugiperda. Expression_system_taxid: 7108. Expression_system_cell_line: sf9. (Invitrogen).

Resolution:

2.40Å R-factor: 0.194 R-free: 0.248

Authors:

B.Ahvazi

Key ref:

B.Ahvazi et al. (2003). Roles of calcium ions in the activation and activity of the transglutaminase 3 enzyme. J Biol Chem, 278, 23834-23841. PubMed id: 12679341 DOI: 10.1074/jbc.M301162200

Date:

31-Jan-03 Release date: 22-Apr-03

Protein chains

Q08188  (TGM3_HUMAN) -  Protein-glutamine gamma-glutamyltransferase E from Homo sapiens

Seq: 693 a.a.

Struc: 675 a.a.*

* PDB and UniProt seqs differ at 4 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.2.3.2.13 - protein-glutamine gamma-glutamyltransferase.
• Reaction: L-glutaminyl-[protein] + L-lysyl-[protein] = [protein]-L-lysyl-N₆-5- L-glutamyl-[protein] + NH4⁺
• Cofactor: Ca(2+)

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

Key reference

DOI no: 10.1074/jbc.M301162200

J Biol Chem 278:23834-23841 (2003)

PubMed id: 12679341

Roles of calcium ions in the activation and activity of the transglutaminase 3 enzyme.

B.Ahvazi, K.M.Boeshans, W.Idler, U.Baxa, P.M.Steinert.

ABSTRACT

The transglutaminase 3 enzyme is widely expressed in many tissues including epithelia. We have shown previously that it can bind three Ca2+ ions, which in site one is constitutively bound, while those in sites two and three are acquired during activation and are required for activity. In particular, binding at site three opens a channel through the enzyme and exposes two tryptophan residues near the active site that are thought to be important for enzyme reaction. In this study, we have solved the structures of three more forms of this enzyme by x-ray crystallography in the presence of Ca2+ and/or Mg2+, which provide new insights on the precise contribution of each Ca2+ ion to activation and activity. First, we found that Ca2+ ion in site one can be exchanged with difficulty, and it has a binding affinity of Kd = 0.3 microm (DeltaH = -6.70 +/- 0.52 kcal/mol), which suggests it is important for the stabilization of the enzyme. Site two can be occupied by some lanthanides but only Ca2+ of the Group 2 family of alkali earth metals, and its occupancy are required for activity. Site three can be occupied by some lanthanides, Ca2+,or Mg2+; however, when Mg2+ is present, the enzyme is inactive, and the channel is closed. Thus Ca2+ binding in both sites two and three cooperate in opening the channel. We speculate that manipulation of the channel opening could be controlled by intracellular cation levels. Together, these data have important implications for reaction mechanism of the enzyme: the opening of a channel perhaps controls access to and manipulation of substrates at the active site.

Selected figure(s)

Figure 1.
FIG. 1. Conformations of the forms I (a and b), II (c and d), and III (e and g) solved in this study. The upper row shows the solved structures of the three forms. This is nominally the front side of the enzyme. The amino-terminal -sandwich (red), catalytic core (blue), -barrel 1 (magenta), and -barrel 2 (orange) domains are shown. The Ca^2^+ ions are shown in yellow, the sole Mg2^+ ion in cyan. Below are shown the electrostatic surface potential images. The acidic and basic residues are colored red and blue, respectively. The electrostatic potentials, including Ca^2^+ and Mg2^+ ions, have been mapped onto the surface plan from -15 kT (deep red) to +15 kT (deep blue). The open channel is clearly evident in b. In g, the back side of the enzyme has a deep cavity; the front side (f) remains closed.

Figure 2.
FIG. 2. Identification of key residues involved in the coordination with metal ions in sites one, two, and three in forms I-III. The details of these interactions and the bond lengths are summarized in Table III.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2003, 278, 23834-23841) copyright 2003.

Figures were selected by an automated process.