Limits...
Interaction of the amyloid precursor protein-like protein 1 (APLP1) E2 domain with heparan sulfate involves two distinct binding modes.

Dahms SO, Mayer MC, Roeser D, Multhaup G, Than ME - Acta Crystallogr. D Biol. Crystallogr. (2015)

Bottom Line: APP and its paralogues APP-like protein 1 (APLP1) and APP-like protein 2 (APLP2) contain the highly conserved heparan sulfate (HS) binding domain E2, which effects various (patho)physiological functions.Terminal binding of APLP1 E2 to heparin specifically involves a structure of the nonreducing end that is very similar to heparanase-processed HS chains.These data reveal a conserved mechanism for the binding of APP-family proteins to HS and imply a specific regulatory role of HS modifications in the biology of APP and APP-like proteins.

View Article: PubMed Central - HTML - PubMed

Affiliation: Protein Crystallography Group, Leibniz Institute for Age Research (FLI), Beutenbergstrasse 11, 07745 Jena, Germany.

ABSTRACT
Beyond the pathology of Alzheimer's disease, the members of the amyloid precursor protein (APP) family are essential for neuronal development and cell homeostasis in mammals. APP and its paralogues APP-like protein 1 (APLP1) and APP-like protein 2 (APLP2) contain the highly conserved heparan sulfate (HS) binding domain E2, which effects various (patho)physiological functions. Here, two crystal structures of the E2 domain of APLP1 are presented in the apo form and in complex with a heparin dodecasaccharide at 2.5 Å resolution. The apo structure of APLP1 E2 revealed an unfolded and hence flexible N-terminal helix αA. The (APLP1 E2)2-(heparin)2 complex structure revealed two distinct binding modes, with APLP1 E2 explicitly recognizing the heparin terminus but also interacting with a continuous heparin chain. The latter only requires a certain register of the sugar moieties that fits to a positively charged surface patch and contributes to the general heparin-binding capability of APP-family proteins. Terminal binding of APLP1 E2 to heparin specifically involves a structure of the nonreducing end that is very similar to heparanase-processed HS chains. These data reveal a conserved mechanism for the binding of APP-family proteins to HS and imply a specific regulatory role of HS modifications in the biology of APP and APP-like proteins.

Show MeSH

Related in: MedlinePlus

Electrostatic interactions of heparin and APLP1 E2. The stereoviews show APLP1 E2 chains a and b in the same orientation. The molecular surface is coloured according to the calculated electrostatic potential, which ranges from red (−10 kT/e−) to blue (+10 kT/e−). Heparin chains are shown as stick models coloured in a gradient according to the crystallographic B factor, which ranges from green (74 Å2) to red (179 Å2). Red arrowheads mark the reducing ends of heparin. (a) Electrostatic interactions of heparin chain a with APLP1 E2. (b) Electrostatic interactions of heparin chain b with APLP1 E2. (c) Structural stabilization of heparan sulfate by APLP1 E2. The dependence of the increase of the melting temperature of APLP1 E2 on the heparin chain length was measured by thermal denaturation assays (Thermofluor assays). The melting temperatures given correspond to the inflection points of the melting curves of APLP1 E2 without heparin and in the presence of saccharides with defined lengths of two (dp2), four (dp4), eight (dp8), 12 (dp12) and 16 (dp16) sugar rings. dp12, which was used for crystallization, is highlighted as a black bar.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4356362&req=5

fig5: Electrostatic interactions of heparin and APLP1 E2. The stereoviews show APLP1 E2 chains a and b in the same orientation. The molecular surface is coloured according to the calculated electrostatic potential, which ranges from red (−10 kT/e−) to blue (+10 kT/e−). Heparin chains are shown as stick models coloured in a gradient according to the crystallographic B factor, which ranges from green (74 Å2) to red (179 Å2). Red arrowheads mark the reducing ends of heparin. (a) Electrostatic interactions of heparin chain a with APLP1 E2. (b) Electrostatic interactions of heparin chain b with APLP1 E2. (c) Structural stabilization of heparan sulfate by APLP1 E2. The dependence of the increase of the melting temperature of APLP1 E2 on the heparin chain length was measured by thermal denaturation assays (Thermofluor assays). The melting temperatures given correspond to the inflection points of the melting curves of APLP1 E2 without heparin and in the presence of saccharides with defined lengths of two (dp2), four (dp4), eight (dp8), 12 (dp12) and 16 (dp16) sugar rings. dp12, which was used for crystallization, is highlighted as a black bar.

Mentions: The heparin chains cover positively charged surface patches of APLP1 E2 (Figs. 5 ▶a and 5 ▶b). Charge equalization mainly contributes to the binding of the negatively charged, extended heparin chain b (Fig. 5 ▶b). However, specific hydrogen bonds are missing at the reducing end of this heparin chain, allowing multiple orientations of negatively charged substituents. Interestingly, the amino acids of the interaction interface of APLP1 E2 and the distant sugar moieties 4b–6b are less well conserved compared with residues involved in specific interactions (Supplementary Fig. S3c). The crystallographic B factors also indicate higher flexibility of the sugar rings 4b, 5b and 6b at the reducing end (Fig. 5 ▶b). As a consequence, poor electron density was observed for several sulfate groups of these sugar residues (Fig. 2 ▶).


Interaction of the amyloid precursor protein-like protein 1 (APLP1) E2 domain with heparan sulfate involves two distinct binding modes.

Dahms SO, Mayer MC, Roeser D, Multhaup G, Than ME - Acta Crystallogr. D Biol. Crystallogr. (2015)

Electrostatic interactions of heparin and APLP1 E2. The stereoviews show APLP1 E2 chains a and b in the same orientation. The molecular surface is coloured according to the calculated electrostatic potential, which ranges from red (−10 kT/e−) to blue (+10 kT/e−). Heparin chains are shown as stick models coloured in a gradient according to the crystallographic B factor, which ranges from green (74 Å2) to red (179 Å2). Red arrowheads mark the reducing ends of heparin. (a) Electrostatic interactions of heparin chain a with APLP1 E2. (b) Electrostatic interactions of heparin chain b with APLP1 E2. (c) Structural stabilization of heparan sulfate by APLP1 E2. The dependence of the increase of the melting temperature of APLP1 E2 on the heparin chain length was measured by thermal denaturation assays (Thermofluor assays). The melting temperatures given correspond to the inflection points of the melting curves of APLP1 E2 without heparin and in the presence of saccharides with defined lengths of two (dp2), four (dp4), eight (dp8), 12 (dp12) and 16 (dp16) sugar rings. dp12, which was used for crystallization, is highlighted as a black bar.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4356362&req=5

fig5: Electrostatic interactions of heparin and APLP1 E2. The stereoviews show APLP1 E2 chains a and b in the same orientation. The molecular surface is coloured according to the calculated electrostatic potential, which ranges from red (−10 kT/e−) to blue (+10 kT/e−). Heparin chains are shown as stick models coloured in a gradient according to the crystallographic B factor, which ranges from green (74 Å2) to red (179 Å2). Red arrowheads mark the reducing ends of heparin. (a) Electrostatic interactions of heparin chain a with APLP1 E2. (b) Electrostatic interactions of heparin chain b with APLP1 E2. (c) Structural stabilization of heparan sulfate by APLP1 E2. The dependence of the increase of the melting temperature of APLP1 E2 on the heparin chain length was measured by thermal denaturation assays (Thermofluor assays). The melting temperatures given correspond to the inflection points of the melting curves of APLP1 E2 without heparin and in the presence of saccharides with defined lengths of two (dp2), four (dp4), eight (dp8), 12 (dp12) and 16 (dp16) sugar rings. dp12, which was used for crystallization, is highlighted as a black bar.
Mentions: The heparin chains cover positively charged surface patches of APLP1 E2 (Figs. 5 ▶a and 5 ▶b). Charge equalization mainly contributes to the binding of the negatively charged, extended heparin chain b (Fig. 5 ▶b). However, specific hydrogen bonds are missing at the reducing end of this heparin chain, allowing multiple orientations of negatively charged substituents. Interestingly, the amino acids of the interaction interface of APLP1 E2 and the distant sugar moieties 4b–6b are less well conserved compared with residues involved in specific interactions (Supplementary Fig. S3c). The crystallographic B factors also indicate higher flexibility of the sugar rings 4b, 5b and 6b at the reducing end (Fig. 5 ▶b). As a consequence, poor electron density was observed for several sulfate groups of these sugar residues (Fig. 2 ▶).

Bottom Line: APP and its paralogues APP-like protein 1 (APLP1) and APP-like protein 2 (APLP2) contain the highly conserved heparan sulfate (HS) binding domain E2, which effects various (patho)physiological functions.Terminal binding of APLP1 E2 to heparin specifically involves a structure of the nonreducing end that is very similar to heparanase-processed HS chains.These data reveal a conserved mechanism for the binding of APP-family proteins to HS and imply a specific regulatory role of HS modifications in the biology of APP and APP-like proteins.

View Article: PubMed Central - HTML - PubMed

Affiliation: Protein Crystallography Group, Leibniz Institute for Age Research (FLI), Beutenbergstrasse 11, 07745 Jena, Germany.

ABSTRACT
Beyond the pathology of Alzheimer's disease, the members of the amyloid precursor protein (APP) family are essential for neuronal development and cell homeostasis in mammals. APP and its paralogues APP-like protein 1 (APLP1) and APP-like protein 2 (APLP2) contain the highly conserved heparan sulfate (HS) binding domain E2, which effects various (patho)physiological functions. Here, two crystal structures of the E2 domain of APLP1 are presented in the apo form and in complex with a heparin dodecasaccharide at 2.5 Å resolution. The apo structure of APLP1 E2 revealed an unfolded and hence flexible N-terminal helix αA. The (APLP1 E2)2-(heparin)2 complex structure revealed two distinct binding modes, with APLP1 E2 explicitly recognizing the heparin terminus but also interacting with a continuous heparin chain. The latter only requires a certain register of the sugar moieties that fits to a positively charged surface patch and contributes to the general heparin-binding capability of APP-family proteins. Terminal binding of APLP1 E2 to heparin specifically involves a structure of the nonreducing end that is very similar to heparanase-processed HS chains. These data reveal a conserved mechanism for the binding of APP-family proteins to HS and imply a specific regulatory role of HS modifications in the biology of APP and APP-like proteins.

Show MeSH
Related in: MedlinePlus