PDBsum entry 3csn

Membrane protein/heme binding protein

PDB id: 3csn

Contents

Protein chains

753 a.a. *

163 a.a. *

Ligands

GOL ×5

Waters ×19

* Residue conservation analysis

PDB id:

3csn

Name:

Membrane protein/heme binding protein

Title:

Structure of the serratia marcescens hemophore receptor hasr in complex with its hemophore hasa

Structure:

Hasr protein. Chain: a, b. Engineered: yes. Hemophore hasa. Chain: c, d. Synonym: heme acquisition system protein a. Engineered: yes

Source:

Serratia marcescens. Gene: hasr. Expressed in: escherichia coli. Gene: hasa.

Resolution:

3.00Å R-factor: 0.219 R-free: 0.244

Authors:

S.Krieg,K.Diederichs

Key ref:

S.Krieg et al. (2009). Heme uptake across the outer membrane as revealed by crystal structures of the receptor-hemophore complex. Proc Natl Acad Sci U S A, 106, 1045-1050. PubMed id: 19144921 DOI: 10.1073/pnas.0809406106

Date:

10-Apr-08 Release date: 20-Jan-09

Protein chains

Q79AD2  (Q79AD2_SERMA) -  HasR protein from Serratia marcescens

Seq: 899 a.a.

Struc: 753 a.a.*

Protein chains

Q54450  (HASA_SERMA) -  Hemophore HasA from Serratia marcescens

Seq: 188 a.a.

Struc: 163 a.a.*

* PDB and UniProt seqs differ at 2 residue positions (black crosses)

DOI no: 10.1073/pnas.0809406106

Proc Natl Acad Sci U S A 106:1045-1050 (2009)

PubMed id: 19144921

Heme uptake across the outer membrane as revealed by crystal structures of the receptor-hemophore complex.

S.Krieg, F.Huché, K.Diederichs, N.Izadi-Pruneyre, A.Lecroisey, C.Wandersman, P.Delepelaire, W.Welte.

ABSTRACT

Gram-negative bacteria use specific heme uptake systems, relying on outer membrane receptors and excreted heme-binding proteins (hemophores) to scavenge and actively transport heme. To unravel the unknown molecular details involved, we present 3 structures of the Serratia marcescens receptor HasR in complex with its hemophore HasA. The transfer of heme over a distance of 9 A from its high-affinity site in HasA into a site of lower affinity in HasR is coupled with the exergonic complex formation of the 2 proteins. Upon docking to the receptor, 1 of the 2 axial heme coordinations of the hemophore is initially broken, but the position and orientation of the heme is preserved. Subsequently, steric displacement of heme by a receptor residue ruptures the other axial coordination, leading to heme transfer into the receptor.

Selected figure(s)

Figure 1.
Structure of the ternary complex HasA∼HasR∼heme. HasA (red) and HasR (cork domain beginning with residue Asn-113 in orange; barrel domain beginning at residue Lys-241 in blue) are indicated as a ribbon model. The first 5 strands and the loops L1–L3 of HasR are omitted to allow a view into the barrel interior. The heme is indicated as a wire frame model (green). The extracellular loops 6–11 are labeled. Yellow parts of or near L6, L8, and L9 mark positions of 6 residue deletions that have been found to abolish HasA binding to the receptor.

Figure 4.
Detail of the HasA∼HasR∼heme complex showing a putative heme access channel extending from the external medium between L3 and the bent loop L4 to the receptor heme-binding site. HasA and HasR are indicated as a CPK model in red and blue, respectively, except for the heme-coordinating HasR histidines that are colored yellow. The heme is indicated as a wire frame model in green and the Fe^3+ atom as a red sphere.

Figures were selected by an automated process.