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Inhibition of insulin fibrillation by osmolytes: Mechanistic insights.

Choudhary S, Kishore N, Hosur RV - Sci Rep (2015)

Bottom Line: We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin.Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation.Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range.

View Article: PubMed Central - PubMed

Affiliation: UM-DAE Centre for Excellence in Basic Sciences, Mumbai University Campus, Mumbai 400098, India.

ABSTRACT
We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin. Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation. Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range. The enthalpies of interaction at various stages of fibrillation process have suggested that the preferential exclusion of the osmolyte and its polar interaction with the protein are important in inhibition. The results indicate that the osmolytes are most effective when added prior to the elongation stage of fibrillation. These observations have significant biological implications, since insulin fibrillation is known to cause injection amyloidosis and our data may help in designing lead drug molecules and development of potential therapeutic strategies.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of mechanism of inhibition of insulin fibrillation by osmolytes.
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f7: Schematic representation of mechanism of inhibition of insulin fibrillation by osmolytes.

Mentions: Amongst betaine, citrulline, proline and sorbitol, the first three osmolytes are seen to effectively inhibit the fibrillation of insulin (Fig. 3). Betaine and citrulline have significantly reduced the extent of fibrillation. On the other hand, proline has not only suppressed but also delayed the fibril formation. ITC results suggest the combined effect of preferential exclusion andspecific interactions by these three osmolytes, leading to inhibition of fibrillation. Looking at the structures of these osmolytes (Fig. 1), it appears that the interactions would be largely electrostatic in nature, although proline can also provide a hydrophobic face from its side chain. The fact that proline is most effective in inhibiting fibrillation seems to suggest that it interferes with the stacking of β-sheets which is, generally, largely driven by hydrophobic interactions. Figure 7 schematically summarizes the model for fibrillation inhibition by the three osmolytes. In the native conditions (in the absence of osmolytes), there is a specific structure of water on the outer surface of the protein. Partial unfolding leads to greater exposure of the protein surface which leads to self-association and fibrillation. In the presence of the osmolytes, two processes can happen: (i) enhanced hydration of the protein surface, strengthening of intra-molecular hydrophobic association, which imparts compactness to the protein, which in turn inhibits inter-molecular hydrophobic association and (ii) direct interaction of osmolytes with the protein surface. Both these factors inhibit fibrillation of the protein. The relative contributions of these two factors will depend upon the structural and chemical characteristics of the individual osmolytes. Certain degree of amorphous aggregation of the partially folded molecules, however, is still possible.


Inhibition of insulin fibrillation by osmolytes: Mechanistic insights.

Choudhary S, Kishore N, Hosur RV - Sci Rep (2015)

Schematic representation of mechanism of inhibition of insulin fibrillation by osmolytes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663473&req=5

f7: Schematic representation of mechanism of inhibition of insulin fibrillation by osmolytes.
Mentions: Amongst betaine, citrulline, proline and sorbitol, the first three osmolytes are seen to effectively inhibit the fibrillation of insulin (Fig. 3). Betaine and citrulline have significantly reduced the extent of fibrillation. On the other hand, proline has not only suppressed but also delayed the fibril formation. ITC results suggest the combined effect of preferential exclusion andspecific interactions by these three osmolytes, leading to inhibition of fibrillation. Looking at the structures of these osmolytes (Fig. 1), it appears that the interactions would be largely electrostatic in nature, although proline can also provide a hydrophobic face from its side chain. The fact that proline is most effective in inhibiting fibrillation seems to suggest that it interferes with the stacking of β-sheets which is, generally, largely driven by hydrophobic interactions. Figure 7 schematically summarizes the model for fibrillation inhibition by the three osmolytes. In the native conditions (in the absence of osmolytes), there is a specific structure of water on the outer surface of the protein. Partial unfolding leads to greater exposure of the protein surface which leads to self-association and fibrillation. In the presence of the osmolytes, two processes can happen: (i) enhanced hydration of the protein surface, strengthening of intra-molecular hydrophobic association, which imparts compactness to the protein, which in turn inhibits inter-molecular hydrophobic association and (ii) direct interaction of osmolytes with the protein surface. Both these factors inhibit fibrillation of the protein. The relative contributions of these two factors will depend upon the structural and chemical characteristics of the individual osmolytes. Certain degree of amorphous aggregation of the partially folded molecules, however, is still possible.

Bottom Line: We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin.Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation.Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range.

View Article: PubMed Central - PubMed

Affiliation: UM-DAE Centre for Excellence in Basic Sciences, Mumbai University Campus, Mumbai 400098, India.

ABSTRACT
We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin. Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation. Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50-250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range. The enthalpies of interaction at various stages of fibrillation process have suggested that the preferential exclusion of the osmolyte and its polar interaction with the protein are important in inhibition. The results indicate that the osmolytes are most effective when added prior to the elongation stage of fibrillation. These observations have significant biological implications, since insulin fibrillation is known to cause injection amyloidosis and our data may help in designing lead drug molecules and development of potential therapeutic strategies.

No MeSH data available.


Related in: MedlinePlus