The aminoacid carboxylated by vitamin K is
Vitamin  K  acts as a coenzyme for the carboxylation  of glutamic  acid residues present in the proteins and this reaction is catalysed by  a  carboxylase (microsomal).
Ref : Satyanarayana, 3rd ed, pg 130
Histidine
Aspartate
Proline
Glutamate