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A cytokine-cytokine interaction in the assembly of higher-order structure and activation of the interleukine-3:receptor complex.

Dey R, Ji K, Liu Z, Chen L - PLoS ONE (2009)

Bottom Line: These observations are consistent with structure-function studies of the GM-CSF:receptor complex showing that formation of the higher-order cytokine:receptor complex is required for signaling.However, a key question not answered from previous studies is how cytokine binding facilitates the assembly of the higher-order complex.Our studies here reveal a potential cytokine-cytokine interaction that participates in the assembly of the dodecamer complex, thus linking cytokine binding to receptor activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Molecular and Computational Biology, University of Southern California, Los Angeles, California, United States of America.

ABSTRACT
Interleukine-3 (IL-3) binds its receptor and initiates a cascade of signaling processes that regulate the proliferation and differentiation of hematopoietic cells. To understand the detailed mechanisms of IL-3 induced receptor activation, we generated a homology model of the IL-3:receptor complex based on the closely related crystal structure of the GM-CSF:receptor complex. Model-predicted interactions between IL-3 and its receptor are in excellent agreement with mutagenesis data, which validate the model and establish a detailed view of IL-3:receptor interaction. The homology structure reveals an IL-3:IL-3 interaction interface in a higher-order complex modeled after the dodecamer of the GM-CSF:receptor complex wherein an analogous GM-CSF:GM-CSF interface is also identified. This interface is mediated by a proline-rich hydrophobic motif (PPLPLL) of the AA' loop that is highly exposed in the structure of isolated IL-3. Various experimental data suggest that this motif is required for IL-3 function through receptor-binding independent mechanisms. These observations are consistent with structure-function studies of the GM-CSF:receptor complex showing that formation of the higher-order cytokine:receptor complex is required for signaling. However, a key question not answered from previous studies is how cytokine binding facilitates the assembly of the higher-order complex. Our studies here reveal a potential cytokine-cytokine interaction that participates in the assembly of the dodecamer complex, thus linking cytokine binding to receptor activation.

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Protein–protein interactions at interface II.(A) A zoom-out view of the interface showing the secondary structural elements of IL-3 and the receptor involved in the reaction. The interaction between Glu22 of IL-3 and a number of aromatic residues from the receptor beta subunit (Tyr39, Tyr365, His367, Tyr421) is shown. (B) A zoom-in view showing additional details of interface II, including the interactions between Met19, Ile77 and Ala73 of IL-3 and Ser102, Val104, Val105 and Thr106 on the receptor beta subunit.
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pone-0005188-g004: Protein–protein interactions at interface II.(A) A zoom-out view of the interface showing the secondary structural elements of IL-3 and the receptor involved in the reaction. The interaction between Glu22 of IL-3 and a number of aromatic residues from the receptor beta subunit (Tyr39, Tyr365, His367, Tyr421) is shown. (B) A zoom-in view showing additional details of interface II, including the interactions between Met19, Ile77 and Ala73 of IL-3 and Ser102, Val104, Val105 and Thr106 on the receptor beta subunit.

Mentions: At interface II (Figure 4), helix A and C of IL-3 bind a composite protein surface formed by the AB and EF loops of domain 1 of one beta subunit and the BC and FG loops of domain 4 of the other. A prominent feature of interface II is the intimate interaction between Glu22 (residues in IL-3 are italicized throughout the text) of IL-3 and a group of aromatic residues of the beta subunit, including Tyr39, Tyr365, His367 and Tyr421 (Figure 4A). In addition to extensive van der Waals contacts, the carboxylate group of Glu22 is in position to form a hydrogen bond with the phenolic hydroxyl group of Tyr421. An adjacent patch of interactions involves Met19, Ser76, Ile77 and Ala73 of IL-3 that pack against Ser102, Val104, Val105 and Thr106 on the beta subunit. Asn15, Asn18, Thr25, and His26 of IL-3 are also in close proximity to contact the beta subunit (Figure 4B). The detailed interactions at interface II are similar to those seen in the GM-CSF:receptor complex but also show some differences. For example, a salt bridge between Lys72 of GM-CSF and Asp107 of the beta subunit is missing at interface II of the IL-3:receptor complex, whereas Ile77 of IL-3 may bind the hydrophobic pocket formed by Ser102, Val104, Val105 and Thr106 of the beta subunit better than the proline counterpart (Pro76) in GM-CSF. The structural features of interface II are consistent with mutagenesis data on the functional roles of interface residues (Figure 1C). For example, the tight packing interaction at the center of the interface is highly sensitive to mutations of Glu22 of IL-3 and Tyr421 of the beta subunit [30], [31], [33], [42], [43]. Even subtle changes, such as substituting Tyr421 with phenylalanine in the beta subunit, abolish the high affinity binding of IL-3 and GM-CSF to the receptor.


A cytokine-cytokine interaction in the assembly of higher-order structure and activation of the interleukine-3:receptor complex.

Dey R, Ji K, Liu Z, Chen L - PLoS ONE (2009)

Protein–protein interactions at interface II.(A) A zoom-out view of the interface showing the secondary structural elements of IL-3 and the receptor involved in the reaction. The interaction between Glu22 of IL-3 and a number of aromatic residues from the receptor beta subunit (Tyr39, Tyr365, His367, Tyr421) is shown. (B) A zoom-in view showing additional details of interface II, including the interactions between Met19, Ile77 and Ala73 of IL-3 and Ser102, Val104, Val105 and Thr106 on the receptor beta subunit.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2662821&req=5

pone-0005188-g004: Protein–protein interactions at interface II.(A) A zoom-out view of the interface showing the secondary structural elements of IL-3 and the receptor involved in the reaction. The interaction between Glu22 of IL-3 and a number of aromatic residues from the receptor beta subunit (Tyr39, Tyr365, His367, Tyr421) is shown. (B) A zoom-in view showing additional details of interface II, including the interactions between Met19, Ile77 and Ala73 of IL-3 and Ser102, Val104, Val105 and Thr106 on the receptor beta subunit.
Mentions: At interface II (Figure 4), helix A and C of IL-3 bind a composite protein surface formed by the AB and EF loops of domain 1 of one beta subunit and the BC and FG loops of domain 4 of the other. A prominent feature of interface II is the intimate interaction between Glu22 (residues in IL-3 are italicized throughout the text) of IL-3 and a group of aromatic residues of the beta subunit, including Tyr39, Tyr365, His367 and Tyr421 (Figure 4A). In addition to extensive van der Waals contacts, the carboxylate group of Glu22 is in position to form a hydrogen bond with the phenolic hydroxyl group of Tyr421. An adjacent patch of interactions involves Met19, Ser76, Ile77 and Ala73 of IL-3 that pack against Ser102, Val104, Val105 and Thr106 on the beta subunit. Asn15, Asn18, Thr25, and His26 of IL-3 are also in close proximity to contact the beta subunit (Figure 4B). The detailed interactions at interface II are similar to those seen in the GM-CSF:receptor complex but also show some differences. For example, a salt bridge between Lys72 of GM-CSF and Asp107 of the beta subunit is missing at interface II of the IL-3:receptor complex, whereas Ile77 of IL-3 may bind the hydrophobic pocket formed by Ser102, Val104, Val105 and Thr106 of the beta subunit better than the proline counterpart (Pro76) in GM-CSF. The structural features of interface II are consistent with mutagenesis data on the functional roles of interface residues (Figure 1C). For example, the tight packing interaction at the center of the interface is highly sensitive to mutations of Glu22 of IL-3 and Tyr421 of the beta subunit [30], [31], [33], [42], [43]. Even subtle changes, such as substituting Tyr421 with phenylalanine in the beta subunit, abolish the high affinity binding of IL-3 and GM-CSF to the receptor.

Bottom Line: These observations are consistent with structure-function studies of the GM-CSF:receptor complex showing that formation of the higher-order cytokine:receptor complex is required for signaling.However, a key question not answered from previous studies is how cytokine binding facilitates the assembly of the higher-order complex.Our studies here reveal a potential cytokine-cytokine interaction that participates in the assembly of the dodecamer complex, thus linking cytokine binding to receptor activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Molecular and Computational Biology, University of Southern California, Los Angeles, California, United States of America.

ABSTRACT
Interleukine-3 (IL-3) binds its receptor and initiates a cascade of signaling processes that regulate the proliferation and differentiation of hematopoietic cells. To understand the detailed mechanisms of IL-3 induced receptor activation, we generated a homology model of the IL-3:receptor complex based on the closely related crystal structure of the GM-CSF:receptor complex. Model-predicted interactions between IL-3 and its receptor are in excellent agreement with mutagenesis data, which validate the model and establish a detailed view of IL-3:receptor interaction. The homology structure reveals an IL-3:IL-3 interaction interface in a higher-order complex modeled after the dodecamer of the GM-CSF:receptor complex wherein an analogous GM-CSF:GM-CSF interface is also identified. This interface is mediated by a proline-rich hydrophobic motif (PPLPLL) of the AA' loop that is highly exposed in the structure of isolated IL-3. Various experimental data suggest that this motif is required for IL-3 function through receptor-binding independent mechanisms. These observations are consistent with structure-function studies of the GM-CSF:receptor complex showing that formation of the higher-order cytokine:receptor complex is required for signaling. However, a key question not answered from previous studies is how cytokine binding facilitates the assembly of the higher-order complex. Our studies here reveal a potential cytokine-cytokine interaction that participates in the assembly of the dodecamer complex, thus linking cytokine binding to receptor activation.

Show MeSH