cat <<eof > mdin
  minimize structure 
 &cntrl
   imin=1, maxcyc=100,
   cut=300.0, igb=2, saltcon=0.2, gbsa=1,
   ntpr=10, ntx=1, ntb=0,
   ntr=1,
 &end
  keep all atoms frozen
  5.0
RES 1 108
END
END
eof
sander   -O -i mdin \
-c trx.crd  -p trx.top  -ref trx.crd -o trx.min.out -r trx.rst