A polypeptide having IgG cysteine protease activity and comprising a variant of the sequence of SEQ ID NO:4 or 5, which variant: (a) is at least 80% identical to SEQ ID NO: 4 or 5; (b) has a cysteine at the position in said variant sequence which corresponds to position 102 of SEQ ID NO: 3; and (c) has, at the positions in said variant sequence which correspond to positions 92, 272, 294 and 296 of SEQ ID NO: 3, a lysine, a histidine, an aspartic acid and an aspartic acid, respectively; wherein said polypeptide is more effective at cleaving human IgG than IdeZ and/or is at least as effective at cleaving human IgG as IdeS; further wherein said variant of the sequence of SEQ ID NO: 4 or 5: has a positively charged amino acid at the position in said variant which corresponds to position 138 of SEQ ID NO: 3, optionally wherein said positively charged amino acid is arginine or lysine; and/or has a positively charged amino acid at the position in said variant which corresponds to position 139 of SEQ ID NO: 3, optionally wherein said positively charged amino acid is arginine or lysine; and/or does not include the contiguous sequence DDYQRNATEA YAKEVPHQIT; and/or has at least one of the following modifications: i. a deletion of the leucine and threonine residues at the positions in said variant which correspond to positions 64 and 65 of SEQ ID NO: 3; ii. a threonine in place of the arginine at the position in said variant which corresponds to position 70 of SEQ ID NO: 3; iii. a deletion of the tyrosine at the position in said variant which corresponds to position 71 of SEQ ID NO: 3; iv. a glutamine in place of the asparagine at the position in said variant which corresponds to position 72 of SEQ ID NO: 3; v. a glycine in place of the asparagine at the position in said variant which corresponds to position 73 of SEQ ID NO: 3; vi. a alanine in place of the glutamic acid at the position in said variant which corresponds to position 67 of SEQ ID NO: 3; vii. a asparagine in place of the glutamine at the position in said variant which corresponds to position 68 of SEQ ID NO: 3. (a) is at least 80% identical to SEQ ID NO: 4 or 5; (b) has a cysteine at the position in said variant sequence which corresponds to position 102 of SEQ ID NO: 3; and (c) has, at the positions in said variant sequence which correspond to positions 92, 272, 294 and 296 of SEQ ID NO: 3, a lysine, a histidine, an aspartic acid and an aspartic acid, respectively; has a positively charged amino acid at the position in said variant which corresponds to position 138 of SEQ ID NO: 3, optionally wherein said positively charged amino acid is arginine or lysine; and/or has a positively charged amino acid at the position in said variant which corresponds to position 139 of SEQ ID NO: 3, optionally wherein said positively charged amino acid is arginine or lysine; and/or does not include the contiguous sequence DDYQRNATEA YAKEVPHQIT; and/or has at least one of the following modifications: i. a deletion of the leucine and threonine residues at the positions in said variant which correspond to positions 64 and 65 of SEQ ID NO: 3; ii. a threonine in place of the arginine at the position in said variant which corresponds to position 70 of SEQ ID NO: 3; iii. a deletion of the tyrosine at the position in said variant which corresponds to position 71 of SEQ ID NO: 3; iv. a glutamine in place of the asparagine at the position in said variant which corresponds to position 72 of SEQ ID NO: 3; v. a glycine in place of the asparagine at the position in said variant which corresponds to position 73 of SEQ ID NO: 3; vi. a alanine in place of the glutamic acid at the position in said variant which corresponds to position 67 of SEQ ID NO: 3; vii. a asparagine in place of the glutamine at the position in said variant which corresponds to position 68 of SEQ ID NO: 3. i. a deletion of the leucine and threonine residues at the positions in said variant which correspond to positions 64 and 65 of SEQ ID NO: 3; ii. a threonine in place of the arginine at the position in said variant which corresponds to position 70 of SEQ ID NO: 3; iii. a deletion of the tyrosine at the position in said variant which corresponds to position 71 of SEQ ID NO: 3; iv. a glutamine in place of the asparagine at the position in said variant which corresponds to position 72 of SEQ ID NO: 3; v. a glycine in place of the asparagine at the position in said variant which corresponds to position 73 of SEQ ID NO: 3; vi. a alanine in place of the glutamic acid at the position in said variant which corresponds to position 67 of SEQ ID NO: 3; vii. a asparagine in place of the glutamine at the position in said variant which corresponds to position 68 of SEQ ID NO: 3.