Structural characterization of the E2 domain of APL-1, a Caenorhabditis elegans homolog of human amyloid precursor protein, and its heparin binding site.

Abstract	The amyloid beta-peptide deposit found in the brain tissue of patients with Alzheimer disease is derived from a large heparin-binding protein precursor APP. The biological function of APP and its homologs is not precisely known. Here we report the x-ray structure of the E2 domain of APL-1, an APP homolog in Caenorhabditis elegans, and compare it to the human APP structure. We also describe the structure of APL-1 E2 in complex with sucrose octasulfate, a highly negatively charged disaccharide, which reveals an unexpected binding pocket between the two halves of E2. Based on the crystal structure, we are able to map, using site-directed mutagenesis, a surface groove on E2 to which heparin may bind. Our biochemical data also indicate that the affinity of E2 for heparin is influenced by pH: at pH 5, the binding appears to be much stronger than that at neutral pH. This property is likely caused by histidine residues in the vicinity of the mapped heparin binding site and could be important for the proposed adhesive function of APL-1.
Authors	James T Hoopes, Xuying Liu, Xiaomeng Xu, Borries Demeler, Ewa Folta-Stogniew, Chris Li, Ya Ha
Journal	The Journal of biological chemistry (J Biol Chem) Vol. 285 Issue 3 Pg. 2165-73 (Jan 15 2010) ISSN: 1083-351X [Electronic] United States
PMID	19906646 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)
Chemical References	APL-1 protein, C elegans Amyloid beta-Protein Precursor Caenorhabditis elegans Proteins Membrane Proteins Solutions Sucrose Heparin sucrose octasulfate
Topics	Amino Acid Sequence Amyloid beta-Protein Precursor (chemistry) Animals Binding Sites Caenorhabditis elegans Caenorhabditis elegans Proteins (chemistry, genetics, metabolism) Crystallography, X-Ray Heparin (metabolism) Humans Hydrogen-Ion Concentration Membrane Proteins (chemistry, genetics, metabolism) Models, Molecular Molecular Sequence Data Mutagenesis, Site-Directed Mutation Protein Stability Protein Structure, Tertiary Sequence Homology, Amino Acid Solutions Sucrose (analogs & derivatives, metabolism)

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