The H13R modification, which substitutes positively charged histidine with arginine of the same charge on Aβ40, increased the rate of fibril formation and the lag time slightly.
With the exception of Lys-A281 and the AMP-moiety-interacting Arg-A317, the previous residues were not well-conserved among the AprA comparative models of SRP and SOB but were substituted by other positively charged residues of varying positions at the opening of the channel (data not shown).
In contrast, H443 can be substituted by a positively charged arginine residue without any effect, even a negatively charged glutamic acid shows moderate (around 50%) influence compared to wild type function.
Next, we substituted the two positively charged amino acids of the TP and - because of its shortness, to exclude an unintentional influence, also the positive charge of the GFP N-terminus (lysine K4) with glutamate by site-directed mutagenesis.
Rooney looked positively ponderous before being substituted and Anthony Martial peripheral, but as Van Gaal admitted what had been Carrick's first words on returning to the dressing room, it was the sort of match United should still have won.
The same effect is seen when the single positively charged residue is substituted by alanine in the model precursors of natural occurring antigenic epitopes LSIINFEKL and LVNVDYSKL (Figure 9), suggesting that this preference for positive charges might be more general.
For Cys, Gly was the most common replacement (25%), while Ala, Val, Ile, Ser, Thr and positively charged Arg all substituted at frequencies of 8 to 12%.
In mutant 1 (Mut-1), six basic residues in the positively charged patch were substituted with alanines (R519, R520, R591, R595, K625 and K626; Supplementary Figure S1B).
To test whether the positive charge of Arg217 was important, we substituted either a glutamate (negatively charged), a lysine residue (positively charged), or an alanine for Arg217.
Another consequence is that positively selected X-linked mutations can, under some conditions, be substituted more rapidly than those on the autosomes.
