Matrix bound SFD mutant TIMP-3 is more stable than wild type TIMP-3.

BACKGROUND

Sorsby's fundus dystrophy (SFD) is a degenerative retinopathy characterised by accumulation of mutant TIMP-3 protein in Bruch's membrane.

AIM

To compare the stability of matrix bound SFD mutant TIMP-3s with wild type TIMP-3.

METHODS

COS-7 cells were transfected with plasmids containing wild type, Ser 181, Gly-167, Ser-156, and Tyr-168 TIMP-3 cDNA. The cells and their matrices were subsequently harvested and homogenised. After measuring the bound wild type and SFD mutant TIMP-3 concentrations by ELISA, aliquots of the homogenates were heated to 100 degrees C. The rates of denaturation of the TIMP proteins at this temperature were monitored by reverse zymography.

RESULTS

Over a period of 24 h at 100 degrees C the biological activity of both wild type and SFD mutant TIMP-3 was lost. Over a period of 6 h at this temperature the biological activity of the SFD mutant TIMP-3s was fully retained whereas that of the wild type TIMP-3 was lost.

CONCLUSION

Matrix bound SFD mutant TIMP-3s are thermodynamically more stable than wild type. This may explain why SFD starts earlier in life than age related macular degeneration.