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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.


Root mean-squared positional deviation among FSH protein backbone atom positions during molecular dynamics simulations computed relative to the original X-ray crystallographic coordinates.A. Comparison of FSH glycoforms decorated with single NAG residues. B. Comparison of FSH glycoforms decorated with TAG oligosaccharides.
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pone.0137897.g004: Root mean-squared positional deviation among FSH protein backbone atom positions during molecular dynamics simulations computed relative to the original X-ray crystallographic coordinates.A. Comparison of FSH glycoforms decorated with single NAG residues. B. Comparison of FSH glycoforms decorated with TAG oligosaccharides.

Mentions: RMSD analysis for the different complexes is reported in Fig 4. In all cases, the structure tends to undergo a minor shift (RMSD > 2.0 Å) within the first 5 ns of simulation, followed by adherence to a relatively stable conformation thereafter. This is a fairly modest level of structural shift that could primarily be ascribed to the difference in simulation temperature (310K) relative to the conditions under which crystal characterization typically is performed (typically less than 100K depending on the precise technique; in this case the precise temperature is not reported for the originating crystal structure [13]). The only other significant impetus for structural relaxation is if a substantial modification is made to the structure that appreciably disrupts the equilibrated balance of forces present in the crystallized structure. Since the originating crystal structure is glycosylated on all four relevant asparagine residues, and since the crystallized glycan on each site is a single NAG residue, it would be normal to expect no substantial structural relaxation of the simulated FSH24(NAG) system. It can thus be considered to be a baseline reference by which to assess structural relaxation by the other systems. We thus find from Fig 4A that none of the other NAG-substituted FSH variants appear to relax in a manner that is qualitatively much different from FSH24(NAG). Furthermore, the introduction of balanced modifications such as removing all four glycans or substituting all four NAG residues with the much larger TAG appendage, seem to have little effect on the overall structural stability of the system. However, the unbalanced FSH15(TAG) structure behaves in a markedly distinct fashion by exhibiting a sharp structural shift between 5–10 ns into the simulation (Fig 4B).


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)

Root mean-squared positional deviation among FSH protein backbone atom positions during molecular dynamics simulations computed relative to the original X-ray crystallographic coordinates.A. Comparison of FSH glycoforms decorated with single NAG residues. B. Comparison of FSH glycoforms decorated with TAG oligosaccharides.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0137897.g004: Root mean-squared positional deviation among FSH protein backbone atom positions during molecular dynamics simulations computed relative to the original X-ray crystallographic coordinates.A. Comparison of FSH glycoforms decorated with single NAG residues. B. Comparison of FSH glycoforms decorated with TAG oligosaccharides.
Mentions: RMSD analysis for the different complexes is reported in Fig 4. In all cases, the structure tends to undergo a minor shift (RMSD > 2.0 Å) within the first 5 ns of simulation, followed by adherence to a relatively stable conformation thereafter. This is a fairly modest level of structural shift that could primarily be ascribed to the difference in simulation temperature (310K) relative to the conditions under which crystal characterization typically is performed (typically less than 100K depending on the precise technique; in this case the precise temperature is not reported for the originating crystal structure [13]). The only other significant impetus for structural relaxation is if a substantial modification is made to the structure that appreciably disrupts the equilibrated balance of forces present in the crystallized structure. Since the originating crystal structure is glycosylated on all four relevant asparagine residues, and since the crystallized glycan on each site is a single NAG residue, it would be normal to expect no substantial structural relaxation of the simulated FSH24(NAG) system. It can thus be considered to be a baseline reference by which to assess structural relaxation by the other systems. We thus find from Fig 4A that none of the other NAG-substituted FSH variants appear to relax in a manner that is qualitatively much different from FSH24(NAG). Furthermore, the introduction of balanced modifications such as removing all four glycans or substituting all four NAG residues with the much larger TAG appendage, seem to have little effect on the overall structural stability of the system. However, the unbalanced FSH15(TAG) structure behaves in a markedly distinct fashion by exhibiting a sharp structural shift between 5–10 ns into the simulation (Fig 4B).

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.