Low fraction of the 222K PrP variant in the protease-resistant moiety of PrPres in heterozygous scrapie positive goats

Abstract

The presence of lysine (K) at codon 222 has been associated with resistance to classical scrapie in goats, but few scrapie cases have been identified in 222Q/K animals. To investigate the contribution of the 222K variant to PrPres formation in natural and experimental Q/K scrapie cases, we applied an immunoblotting method based on the use of two different monoclonal antibodies, F99/97.6.1 and SAF84, chosen for their different affinities to 222K and 222Q PrP variants. Our finding that PrPres seems to be formed nearly totally by the 222Q variant provides evidence that the 222K PrP variant confers resistance to conversion to PrPres formation and reinforces the view that this mutation has a protective role against classical scrapie in goats.

Fig. 1.

Western blot analysis of proteinase K-treated PrP^res extracted from the brain tissue of French (panel 1; experimental scrapie isolates), Greek and Italian goats (panel 2; natural scrapie cases) and no-pK treated PrP^C (panel 3; negative samples) with different polymorphisms at PrP codon 222 (222Q/Q,222Q/K and 222 K/K). PrP^res and PrP^C were detected in parallel by F99/97.6.1 (a) and SAF84 (b).

Fig. 2.

Scatter plot of the F99/SAF84 ratio obtained from Greek, French and Italian goat samples showing different genotypes at PRNP gene codon 222 (222Q/Q, 222Q/K and 222 K/K). Crosses indicate the average F99/SAF84 ratio for each sample with standard deviation (vertical lines).