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Biophys J, December 2002, p. 3513-3524, Vol. 83, No. 6


and
*Department of Medical Biochemistry, Federal University of Rio de
Janeiro, Rio de Janeiro RJ 21944-590, Brazil;
Instituto
de Física "Gleb Wataghin," Unicamp, Campinas SP 13084-971, Brazil; and
Laboratório Nacional de Luz
Síncrotron (LNLS), Campinas SP 13084-9701, Brazil
The amyloid precursor protein (APP) is the precursor of
the
-amyloid peptide (A
), which is centrally related to the
genesis of Alzheimer's disease (AD). In addition, APP has been
suggested to mediate and/or participate in events that lead to neuronal degeneration in AD. Despite the fact that various aspects of the cell
biology of APP have been investigated, little information on the
structure of this protein is available. In this work, the solution
structure of the soluble extracellular domain of APP (sAPP, composing
89% of the amino acid residues of the whole protein) has been
investigated through a combination of size-exclusion chromatography,
circular dichroism, and synchrotron radiation small-angle x-ray
scattering (SAXS) studies. sAPP is monomeric in solution (65 kDa
obtained from SAXS measurements) and exhibits an anisometric molecular
shape, with a Stokes radius of 39 or 51 Å calculated from SAXS or
chromatographic data, respectively. The radius of gyration and the
maximum molecular length obtained by SAXS were 38 Å and 130 Å,
respectively. Analysis of SAXS data further allowed building a
structural model for sAPP in solution. Circular dichroism data and
secondary structure predictions based on the amino acid sequence of APP
suggested that a significant fraction of APP (30% of the amino acid
residues) is not involved in standard secondary structure elements,
which may explain the elongated shape of the molecule recovered in our
structural model. Possible implications of the structure of APP in
ligand binding and molecular recognition events involved in the
biological functions of this protein are discussed.
Biophys J, December 2002, p. 3513-3524, Vol. 83, No. 6
© 2002 by the Biophysical Society 0006-3495/02/12/3513/12 $2.00
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