4LBF: Crystal Structure Of Human Alpha-defensin 1 (hnp1) I20a/l25a Mutant

HNP1 is a human alpha defensin that forms dimers and multimers governed by hydrophobic residues, including Tyr(16), Ile(20), Leu(25), and Phe(28). Previously, alanine scanning mutagenesis identified each of these residues and other hydrophobic residues as important for function. Here we report further structural and functional studies of residues shown to interact with one another across oligomeric interfaces: I20A-HNP1 and L25A-HNP1, plus the double alanine mutants I20A/L25A-HNP1 and Y16A/F28A-HNP1, and the quadruple alanine mutant Y16A/I20A/L25A/F28A-HNP1. We tested binding to HIV-1 gp120 and HNP1 by surface plasmon resonance, binding to HIV-1 gp41 and HNP1 by fluorescence polarization, inhibition of anthrax lethal factor, and antibacterial activity using the virtual colony count assay. Similar to the previously described single mutant W26A-HNP1, the quadruple mutant displayed the least activity in all functional assays, followed by the double mutant Y16A/F28A-HNP1. The effects of the L25A and I20A single mutations were milder than the double mutant I20A/L25A-HNP1. Crystallographic studies confirmed the correct folding and disulfide pairing, and depicted an array of dimeric and tetrameric structures. These results indicate that side chain hydrophobicity is the critical factor that determines activity at these positions.
PDB ID: 4LBFDownload
MMDB ID: 115480
PDB Deposition Date: 2013/6/20
Updated in MMDB: 2013/11
Experimental Method:
x-ray diffraction
Resolution: 1.7  Å
Source Organism:
Similar Structures:
Biological Unit for 4LBF: tetrameric; determined by author and by software (PISA)
Molecular Components in 4LBF
Label Count Molecule
Proteins (4 molecules)
Neutrophil Defensin 1(Gene symbol: DEFA1)
Molecule annotation
Chemical (1 molecule)
* Click molecule labels to explore molecular sequence information.

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