Crystal Structure of SPLUNC1 Disulfide Mutant M2 (A48C, V253C)

Experimental Data Snapshot

  • Resolution: 2.60 Å
  • R-Value Free: 0.284 
  • R-Value Work: 0.220 
  • R-Value Observed: 0.226 

wwPDB Validation   3D Report Full Report

This is version 1.4 of the entry. See complete history


Structural Features Essential to the Antimicrobial Functions of Human SPLUNC1.

Walton, W.G.Ahmad, S.Little, M.S.Kim, C.S.Tyrrell, J.Lin, Q.Di, Y.P.Tarran, R.Redinbo, M.R.

(2016) Biochemistry 55: 2979-2991

  • DOI: https://doi.org/10.1021/acs.biochem.6b00271
  • Primary Citation of Related Structures:  
    5I7J, 5I7K, 5I7L

  • PubMed Abstract: 

    SPLUNC1 is an abundantly secreted innate immune protein in the mammalian respiratory tract that exerts bacteriostatic and antibiofilm effects, binds to lipopolysaccharide (LPS), and acts as a fluid-spreading surfactant. Here, we unravel the structural elements essential for the surfactant and antimicrobial functions of human SPLUNC1 (short palate lung nasal epithelial clone 1). A unique α-helix (α4) that extends from the body of SPLUNC1 is required for the bacteriostatic, surfactant, and LPS binding activities of this protein. Indeed, we find that mutation of just four leucine residues within this helical motif to alanine is sufficient to significantly inhibit the fluid spreading abilities of SPLUNC1, as well as its bacteriostatic actions against Gram-negative pathogens Burkholderia cenocepacia and Pseudomonas aeruginosa. Conformational flexibility in the body of SPLUNC1 is also involved in the bacteriostatic, surfactant, and LPS binding functions of the protein as revealed by disulfide mutants introduced into SPLUNC1. In addition, SPLUNC1 exerts antibiofilm effects against Gram-negative bacteria, although α4 is not involved in this activity. Interestingly, though, the introduction of surface electrostatic mutations away from α4 based on the unique dolphin SPLUNC1 sequence, and confirmed by crystal structure, is shown to impart antibiofilm activity against Staphylococcus aureus, the first SPLUNC1-dependent effect against a Gram-positive bacterium reported to date. Together, these data pinpoint SPLUNC1 structural motifs required for the antimicrobial and surfactant actions of this protective human protein.

  • Organizational Affiliation

    Departments of Chemistry, Biochemistry, and Microbiology, University of North Carolina , 4350 Genome Sciences Building, Chapel Hill, North Carolina 27599-3290, United States.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
BPI fold-containing family A member 1
A, B
240Homo sapiensMutation(s): 2 
UniProt & NIH Common Fund Data Resources
Find proteins for Q9NP55 (Homo sapiens)
Explore Q9NP55 
Go to UniProtKB:  Q9NP55
GTEx:  ENSG00000198183 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ9NP55
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.60 Å
  • R-Value Free: 0.284 
  • R-Value Work: 0.220 
  • R-Value Observed: 0.226 
  • Space Group: C 2 2 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 47.083α = 90
b = 203.588β = 90
c = 120.211γ = 90
Software Package:
Software NamePurpose
DENZOdata reduction
SCALEPACKdata scaling

Structure Validation

View Full Validation Report

Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
National Institutes of Health/National Heart, Lung, and Blood Institute (NIH/NHLBI)United StatesR01 HL108927

Revision History  (Full details and data files)

  • Version 1.0: 2016-05-18
    Type: Initial release
  • Version 1.1: 2016-06-08
    Changes: Database references
  • Version 1.2: 2017-09-20
    Changes: Author supporting evidence, Database references, Derived calculations
  • Version 1.3: 2019-12-04
    Changes: Author supporting evidence
  • Version 1.4: 2023-09-27
    Changes: Data collection, Database references, Refinement description