PDBsum entry 1s6e

Membrane protein

PDB id: 1s6e

Contents

Protein chain

224 a.a.

Theoretical model

PDB id:

1s6e

Name:

Membrane protein

Title:

Theoreticaly modeled structure for human porin 6 protein

Structure:

Aquaporin 6. Chain: a. Synonym: aquaporin-2 like, hkid

Source:

Homo sapiens. Human. Tissue: kidney

Authors:

S.Arun Kumar

Key ref:

T.Jabeen et al. (2005). Crystal structure of a calcium-induced dimer of two isoforms of cobra phospholipase A2 at 1.6 A resolution. Proteins, 59, 856-863. PubMed id: 15828003 DOI: 10.1002/prot.20464

Date:

23-Jan-04 Release date: 17-Feb-04

Protein chain

Q13520  (AQP6_HUMAN) -  Aquaporin-6

Seq: 282 a.a.

Struc: 224 a.a.*

* PDB and UniProt seqs differ at 3 residue positions (black crosses)

DOI no: 10.1002/prot.20464

Proteins 59:856-863 (2005)

PubMed id: 15828003

Crystal structure of a calcium-induced dimer of two isoforms of cobra phospholipase A2 at 1.6 A resolution.

T.Jabeen, S.Sharma, N.Singh, R.K.Singh, P.Kaur, M.Perbandt, C.h.Betzel, A.Srinivasan, T.P.Singh.

ABSTRACT

The calcium-induced formation of a complex between two isoforms of cobra venom phospholipase A2 reveals a novel interplay between the monomer-dimer and activity-inactivity transitions. The monodispersed isoforms lack activity in the absence of calcium ions while both molecules gain activity in the presence of calcium ions. At concentrations higher than 10 mg/ml, in the presence of calcium ions, they dimerize and lose activity again. The present study reports the crystal structure of a calcium-induced dimer between two isoforms of cobra phospholipase A2. In the complex, one molecule contains a calcium ion in the calcium binding loop while the second molecule does not possess an intramolecular calcium ion. However, there are two calcium ions per dimer in the structure. The second calcium ion is present at an intermolecular site and that is presumably responsible for the dimerization. The calcium binding loops of the two molecules adopt strikingly different conformations. The so-called calcium binding loop in the calcium-containing molecule adopts a normal conformation as generally observed in other calcium containing phospholipase A(2) enzymes while the conformation of the corresponding loop in the calcium free monomer deviates considerably with the formation of a unique intraloop Gly33 (N)-Cys27 (O) = 2.74 A backbone hydrogen bond. The interactions of Arg31 (B) with Asp49 (A) and absence of calcium ion are responsible for the loss of catalytic activity in molecule A while interactions of Arg2 (B) with Tyr52 (B) inactivate molecule B.

Selected figure(s)

Figure 3.
Figure 3. PLA[2] activity with varying calcium ion concentration. The molar ratio of enzyme and calcium is shown on the X-axis while the percent activity is indicated on Y-axis.

Figure 5.
Figure 5. A: Calcium binding loop of molecule B with the final |2F[o] - Fc| electron density for the calcium ion drawn at 4 . The calcium coordinations with loop residues, Asp 49, phosphate ion and the water molecule are also indicated. B: Superposition of the calcium binding loops of molecules A (green) and B (yellow). The calcium free loop of molecule A adopts a narrow conformation. C: Calcium binding loop of molecule A. The arginine 31 from molecule B is also shown. The intraloop hydrogen bond between Cys27 O and Gly33 N is indicated by green dotted line. D: The final |2F[o] - Fc| electron density for the calcium ion drawn at 4 at the interface of the two molecules. Calcium coordinated intermolecular interactions are indicated by dotted lines. The coordination is sevenfold with trigonal bipyramidal geometry.

The above figures are reprinted by permission from John Wiley & Sons, Inc.: Proteins (2005, 59, 856-863) copyright 2005.

Figures were selected by an automated process.