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Glycosylation Effects on FSH-FSHR Interaction Dynamics: A Case Study of Different FSH Glycoforms by Molecular Dynamics Simulations.

Meher BR, Dixit A, Bousfield GR, Lushington GH - PLoS ONE (2015)

Bottom Line: However, substantial qualitative differences emerge between FSH15 and FSH24 when FSH is decorated with a much larger, tetra-antennary glycan.Specifically, the FSHR complex with hypo-glycosylated FSH15 is observed to undergo a significant conformational shift after 5-10 ns of simulation, indicating that FSH15 has greater conformational flexibility than FSH24 which may explain the more favorable FSH15 kinetic profile.FSH15 also exhibits a stronger binding free energy, due in large part to formation of closer and more persistent salt-bridges with FSHR.

View Article: PubMed Central - PubMed

Affiliation: Bioinformatics Core Facility, University of Kansas, Lawrence, Kansas, United States of America.

ABSTRACT
The gonadotropin known as follicle-stimulating hormone (FSH) plays a key role in regulating reproductive processes. Physiologically active FSH is a glycoprotein that can accommodate glycans on up to four asparagine residues, including two sites in the FSHα subunit that are critical for biochemical function, plus two sites in the β subunit, whose differential glycosylation states appear to correspond to physiologically distinct functions. Some degree of FSHβ hypo-glycosylation seems to confer advantages toward reproductive fertility of child-bearing females. In order to identify possible mechanistic underpinnings for this physiological difference we have pursued computationally intensive molecular dynamics simulations on complexes between the high affinity site of the gonadal FSH receptor (FSHR) and several FSH glycoforms including fully-glycosylated (FSH24), hypo-glycosylated (e.g., FSH15), and completely deglycosylated FSH (dgFSH). These simulations suggest that deviations in FSH/FSHR binding profile as a function of glycosylation state are modest when FSH is adorned with only small glycans, such as single N-acetylglucosamine residues. However, substantial qualitative differences emerge between FSH15 and FSH24 when FSH is decorated with a much larger, tetra-antennary glycan. Specifically, the FSHR complex with hypo-glycosylated FSH15 is observed to undergo a significant conformational shift after 5-10 ns of simulation, indicating that FSH15 has greater conformational flexibility than FSH24 which may explain the more favorable FSH15 kinetic profile. FSH15 also exhibits a stronger binding free energy, due in large part to formation of closer and more persistent salt-bridges with FSHR.

No MeSH data available.


Comparison of FSH dynamic structural features at the FSH/FSHR interface for FSH(TAG) glycoforms.A. FSH15(TAG) and B. FSH24(TAG). The protein portion of FSH is rendered in ribbon form, while the spatial extent of TAG glycan residues is shown via transparent green features. FSH ribbons are colored as follows: blue = FSH residues with FSHR contact surfaces; red = FSH residues with backbone RMSD shifts of greater than 1.5 Å; purple = FSH residues with FSHR contact surfaces and backbone RMSD shifts of greater than 1.5 Å.
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pone.0137897.g005: Comparison of FSH dynamic structural features at the FSH/FSHR interface for FSH(TAG) glycoforms.A. FSH15(TAG) and B. FSH24(TAG). The protein portion of FSH is rendered in ribbon form, while the spatial extent of TAG glycan residues is shown via transparent green features. FSH ribbons are colored as follows: blue = FSH residues with FSHR contact surfaces; red = FSH residues with backbone RMSD shifts of greater than 1.5 Å; purple = FSH residues with FSHR contact surfaces and backbone RMSD shifts of greater than 1.5 Å.

Mentions: It can be noted from Fig 4B that over the course of a full 40 ns simulation, the overall RMSD of FSH24(TAG) and dgFSH eventually attain a level comparable to FSH15(TAG), however, the distribution of positional deviation in FSH15(TAG) is not equivalent to FSH24(TAG). As shown in Fig 5A and 5B, we find that the precise glycosylation state has a substantial effect in determining which specific residues exhibit the greatest shifts relative to the original crystal structure. Regardless of glycosylation state, the percentage of residues that exhibit backbone RMSD shifts of greater than 1.5 Å from the equilibrated positions is relatively small. Nearly all of the overall variation that is observed in each structure occurs on a solvent exposed surface, and within that subset the predominant fraction of total variation is localized mostly either in flexible loops and chain termini. Relatively few high mobility residues are found in close proximity to the FSH/FSHR interface where they would have the greatest influence on FSH binding kinetics. In the case of residues located at or near the FSH24(TAG)/FSHR interface, only Lys40 and Ala43 (both in FSHβ) exhibit positional shifts of greater than 1.5 Å, while for the FSH15(TAG)/FSHR interface that list includes Lys40, Ala43, Asp88, and Ser89 in FSHβ plus Met47, Leu48 and Val49 in FSHα.


Glycosylation Effects on FSH-FSHR Interaction Dynamics: A Case Study of Different FSH Glycoforms by Molecular Dynamics Simulations.

Meher BR, Dixit A, Bousfield GR, Lushington GH - PLoS ONE (2015)

Comparison of FSH dynamic structural features at the FSH/FSHR interface for FSH(TAG) glycoforms.A. FSH15(TAG) and B. FSH24(TAG). The protein portion of FSH is rendered in ribbon form, while the spatial extent of TAG glycan residues is shown via transparent green features. FSH ribbons are colored as follows: blue = FSH residues with FSHR contact surfaces; red = FSH residues with backbone RMSD shifts of greater than 1.5 Å; purple = FSH residues with FSHR contact surfaces and backbone RMSD shifts of greater than 1.5 Å.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581761&req=5

pone.0137897.g005: Comparison of FSH dynamic structural features at the FSH/FSHR interface for FSH(TAG) glycoforms.A. FSH15(TAG) and B. FSH24(TAG). The protein portion of FSH is rendered in ribbon form, while the spatial extent of TAG glycan residues is shown via transparent green features. FSH ribbons are colored as follows: blue = FSH residues with FSHR contact surfaces; red = FSH residues with backbone RMSD shifts of greater than 1.5 Å; purple = FSH residues with FSHR contact surfaces and backbone RMSD shifts of greater than 1.5 Å.
Mentions: It can be noted from Fig 4B that over the course of a full 40 ns simulation, the overall RMSD of FSH24(TAG) and dgFSH eventually attain a level comparable to FSH15(TAG), however, the distribution of positional deviation in FSH15(TAG) is not equivalent to FSH24(TAG). As shown in Fig 5A and 5B, we find that the precise glycosylation state has a substantial effect in determining which specific residues exhibit the greatest shifts relative to the original crystal structure. Regardless of glycosylation state, the percentage of residues that exhibit backbone RMSD shifts of greater than 1.5 Å from the equilibrated positions is relatively small. Nearly all of the overall variation that is observed in each structure occurs on a solvent exposed surface, and within that subset the predominant fraction of total variation is localized mostly either in flexible loops and chain termini. Relatively few high mobility residues are found in close proximity to the FSH/FSHR interface where they would have the greatest influence on FSH binding kinetics. In the case of residues located at or near the FSH24(TAG)/FSHR interface, only Lys40 and Ala43 (both in FSHβ) exhibit positional shifts of greater than 1.5 Å, while for the FSH15(TAG)/FSHR interface that list includes Lys40, Ala43, Asp88, and Ser89 in FSHβ plus Met47, Leu48 and Val49 in FSHα.

Bottom Line: However, substantial qualitative differences emerge between FSH15 and FSH24 when FSH is decorated with a much larger, tetra-antennary glycan.Specifically, the FSHR complex with hypo-glycosylated FSH15 is observed to undergo a significant conformational shift after 5-10 ns of simulation, indicating that FSH15 has greater conformational flexibility than FSH24 which may explain the more favorable FSH15 kinetic profile.FSH15 also exhibits a stronger binding free energy, due in large part to formation of closer and more persistent salt-bridges with FSHR.

View Article: PubMed Central - PubMed

Affiliation: Bioinformatics Core Facility, University of Kansas, Lawrence, Kansas, United States of America.

ABSTRACT
The gonadotropin known as follicle-stimulating hormone (FSH) plays a key role in regulating reproductive processes. Physiologically active FSH is a glycoprotein that can accommodate glycans on up to four asparagine residues, including two sites in the FSHα subunit that are critical for biochemical function, plus two sites in the β subunit, whose differential glycosylation states appear to correspond to physiologically distinct functions. Some degree of FSHβ hypo-glycosylation seems to confer advantages toward reproductive fertility of child-bearing females. In order to identify possible mechanistic underpinnings for this physiological difference we have pursued computationally intensive molecular dynamics simulations on complexes between the high affinity site of the gonadal FSH receptor (FSHR) and several FSH glycoforms including fully-glycosylated (FSH24), hypo-glycosylated (e.g., FSH15), and completely deglycosylated FSH (dgFSH). These simulations suggest that deviations in FSH/FSHR binding profile as a function of glycosylation state are modest when FSH is adorned with only small glycans, such as single N-acetylglucosamine residues. However, substantial qualitative differences emerge between FSH15 and FSH24 when FSH is decorated with a much larger, tetra-antennary glycan. Specifically, the FSHR complex with hypo-glycosylated FSH15 is observed to undergo a significant conformational shift after 5-10 ns of simulation, indicating that FSH15 has greater conformational flexibility than FSH24 which may explain the more favorable FSH15 kinetic profile. FSH15 also exhibits a stronger binding free energy, due in large part to formation of closer and more persistent salt-bridges with FSHR.

No MeSH data available.