PDBsum entry 4wre

Sugar binding protein

PDB id: 4wre

Contents

Protein chain

136 a.a.

Ligands

INS

HEZ

Metals

_CL

_CA ×2

Waters ×87

PDB id:

4wre

Name:

Sugar binding protein

Title:

Crystal structure of surfactant protein-a dedn mutant (e171d/p175e/r197n/k203d) complexed with inositol

Structure:

Pulmonary surfactant-associated protein a. Chain: a. Fragment: neck and carbohydrate recognition domain. Synonym: sp-a. Engineered: yes. Mutation: yes

Source:

Rattus norvegicus. Rat. Organism_taxid: 10116. Gene: sftpa1, sftp-1, sftp1, sftpa. Expressed in: trichoplusia ni. Expression_system_taxid: 7111.

Resolution:

1.75Å R-factor: 0.191 R-free: 0.222

Authors:

M.J.Rynkiewicz,H.Wu,T.R.Cafarella,N.M.Nikolaidis,J.F.Head,B.A.Seaton, F.X.Mccormack

Key ref:

M.J.Rynkiewicz et al. (2017). Differential Ligand Binding Specificities of the Pulmonary Collectins Are Determined by the Conformational Freedom of a Surface Loop. Biochemistry, 56, 4095-4105. PubMed id: 28719181 DOI: 10.1021/acs.biochem.6b01313

Date:

23-Oct-14 Release date: 10-Feb-16

Protein chain

P08427  (SFTPA_RAT) -  Pulmonary surfactant-associated protein A from Rattus norvegicus

Seq: 248 a.a.

Struc: 136 a.a.*

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

DOI no: 10.1021/acs.biochem.6b01313

Biochemistry 56:4095-4105 (2017)

PubMed id: 28719181

Differential Ligand Binding Specificities of the Pulmonary Collectins Are Determined by the Conformational Freedom of a Surface Loop.

M.J.Rynkiewicz, H.Wu, T.R.Cafarella, N.M.Nikolaidis, J.F.Head, B.A.Seaton, F.X.McCormack.

ABSTRACT

Lung surfactant proteins (SPs) play critical roles in surfactant function and innate immunity. SP-A and SP-D, members of the collectin family of C-type lectins, exhibit distinct ligand specificities, effects on surfactant structure, and host defense functions despite extensive structural homology. SP-A binds to dipalmitoylphosphatidylcholine (DPPC), the major surfactant lipid component, but not phosphatidylinositol (PI), whereas SP-D shows the opposite preference. Additionally, SP-A and SP-D recognize widely divergent pathogen-associated molecular patterns. Previous studies suggested that a ligand-induced surface loop conformational change unique to SP-A contributes to lipid binding affinity. To test this hypothesis and define the structural features of SP-A and SP-D that determine their ligand binding specificities, a structure-guided approach was used to introduce key features of SP-D into SP-A. A quadruple mutant (E171D/P175E/R197N/K203D) that introduced an SP-D-like loop-stabilizing calcium binding site into the carbohydrate recognition domain was found to interconvert SP-A ligand binding preferences to an SP-D phenotype, exchanging DPPC for PI specificity, and resulting in the loss of lipid A binding and the acquisition of more avid mannan binding properties. Mutants with constituent single or triple mutations showed alterations in their lipid and sugar binding properties that were intermediate between those of SP-A and SP-D. Structures of mutant complexes with inositol or methyl-mannose revealed an attenuation of the ligand-induced conformational change relative to wild-type SP-A. These studies suggest that flexibility in a key surface loop supports the distinctive lipid binding functions of SP-A, thus contributing to its multiple functions in surfactant structure and regulation, and host defense.