Alkyl and Aryl Transferases/chemistry; Artemisia annua/enzymology; Artemisinins/metabolism; Plant Proteins/chemistry; Alkyl and Aryl Transferases/genetics; Alkyl and Aryl Transferases/metabolism; Amino Acid Sequence; Amino Acid Substitution; Artemisia annua/genetics; Biocatalysis; Catalytic Domain; Crystallography, X-Ray; Escherichia coli/genetics; Leucine/chemistry; Leucine/genetics; Leucine/metabolism; Models, Molecular; Molecular Sequence Data; Monocyclic Sesquiterpenes; Plant Proteins/genetics; Plant Proteins/metabolism; Protein Engineering; Recombinant Proteins/chemistry; Recombinant Proteins/genetics; Recombinant Proteins/metabolism; Sequence Alignment; Sequence Homology, Amino Acid; Serine/chemistry; Serine/genetics; Serine/metabolism; Sesquiterpenes/metabolism; Structure-Activity Relationship; Threonine/chemistry; Threonine/genetics; Threonine/metabolism