Cedilla-accented "s" (ş) not working with tufte-latex AND MinionPro (other cedilla-accented characters do work)

I want to typeset the characters ş and Ş using the tufte-book document class and the Minion Pro font. The composed characters c{s} and c{S} work fine if I use either of the two packages but not if I use both packages at the same time, as seen in the following examples. For all the examples I also show c{c} (ç) and c{C} (Ç) which seem to work just fine in either case!

Not working as intended:

documentclass{tufte-book}
usepackage{MinionPro}

begin{document}
c{s} c{S} c{c} c{C} 
end{document}

produces

Only tufte-book works:

documentclass{tufte-book}

begin{document}
c{s} c{S} c{c} c{C} 
end{document}

produces

Only MinionPro (with documentclass{article}) works as well:

documentclass{article}
usepackage{MinionPro}

begin{document}
c{s} c{S} c{c} c{C}
end{document}

produces

I cannot find out where both packages clash. Thanks for your help.

documentclass[nofonts]{tufte-book}

usepackage{MinionPro}

begin{document}
c{s} c{S} c{c} c{C}
end{document}