sentence: To our knowledge , there are only four phosphohistidine phosphatases for which in vivo targets have been proposed : SixA in Escherichia coli and PHPT1 , PGAM5 , and LHPP in mammals ( 21 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ) .