The present invention provides novel methods for preparing glycosylated molecules such as oligosaccharides, glycolipids, and glycoproteins/peptides. Novel sialyltransferases are also disclosed. The method includes forming a reaction mixture containing an acceptor molecule, a donor substrate having a sugar moiety and a nucleotide, and a sialyltransferase selected from PmST3 (SEQ ID NO:7) and certain variants thereof. The reaction mixture is formed under conditions sufficient to transfer the sugar moiety from the donor substrate to the acceptor molecule, thereby forming the glycosylated molecule. In some embodiments, the acceptor molecule is selected from a natural product, an oligosaccharide, a glycoprotein, and a glycolipid. In some embodiments, the donor substrate is formed via conversion of a suitable hexosamine derivative to a cytidine 5′-monophosphate(CMP)-sialic acid in a one-pot reaction mixture containing asialic acid aldolase and a CMP-sialic acid synthetase.