A polypeptide having proline-specific endoprotease activity, wherein the polypeptide is selected from the group consisting of: i. a polypeptide, which has at least 91% identity to the amino acid sequence according to SEQ ID NO: 1, and which, when aligned with an amino acid sequence according to SEQ ID NO: 1 comprises an amino acid selected from the group consisting of Ala, Cys, Asp, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Gln, Arg, Ser, Thr, Val, Trp, and Tyr at a position corresponding to position 469, and optionally an amino acid of Phe at position 204, Ser at position 304, Ala at position 377, Thr at position 466 and / or Ala at position 477, wherein the position is defined with reference to SEQ ID NO:1; ii. a polypeptide comprising an amino acid sequence according to SEQ ID NO: 1, wherein SEQ ID NO: 1 comprises at least one amino acid substitution selected from the group consisting of P469A, P469C, P469D, P469F, P469G, P469H, P469I, P469K, P469L, P469M, P469N, P469Q, P469R, P469S, P469T, P469V, P469W, and P469Y, and optionally an amino acid substitution I204F, P304S, P377A, P466T, and / or P477A, wherein the amino acid substitution is defined with reference to SEQ ID NO: 1; iii. a polypeptide according to i) to ii), but lacking a signal sequence and/or a proprotein sequence; iv. a polypeptide according to ii) or iii), wherein the polypeptide has at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to the amino acid sequence according to SEQ ID NO: 1; and, v. a polypeptide encoded by a nucleic acid which has at 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 2, or to a mature coding sequence of SEQ ID NO: 2, wherein SEQ ID NO: 2 comprises at least one mutation encoding at least an amino acid substitution selected from the group P469A, P469C, P469D, P469F, P469G, P469H, P469I, P469K, P469L, P469M, P469N, P469Q, P469R, P469S, P469T, P469V, P469W, and P469Y, and optionally wherein SEQ ID NO: 2 comprises at least one further mutation encoding an amino acid substitution I204F, P304S, P377A, P466T, and / or P477A wherein the amino acid substitutions are defined with reference to SEQ ID NO: 1, wherein the polypeptide has less than 70% residual activity on acetyl-AlaAlaPro-paranitroaniline (Ac-AAP-pNA) as a substrate after the polypeptide has been kept at a temperature of 65°C for 15 min. i. a polypeptide, which has at least 91% identity to the amino acid sequence according to SEQ ID NO: 1, and which, when aligned with an amino acid sequence according to SEQ ID NO: 1 comprises an amino acid selected from the group consisting of Ala, Cys, Asp, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Gln, Arg, Ser, Thr, Val, Trp, and Tyr at a position corresponding to position 469, and optionally an amino acid of Phe at position 204, Ser at position 304, Ala at position 377, Thr at position 466 and / or Ala at position 477, wherein the position is defined with reference to SEQ ID NO:1; ii. a polypeptide comprising an amino acid sequence according to SEQ ID NO: 1, wherein SEQ ID NO: 1 comprises at least one amino acid substitution selected from the group consisting of P469A, P469C, P469D, P469F, P469G, P469H, P469I, P469K, P469L, P469M, P469N, P469Q, P469R, P469S, P469T, P469V, P469W, and P469Y, and optionally an amino acid substitution I204F, P304S, P377A, P466T, and / or P477A, wherein the amino acid substitution is defined with reference to SEQ ID NO: 1; iii. a polypeptide according to i) to ii), but lacking a signal sequence and/or a proprotein sequence; iv. a polypeptide according to ii) or iii), wherein the polypeptide has at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to the amino acid sequence according to SEQ ID NO: 1; and, v. a polypeptide encoded by a nucleic acid which has at 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 2, or to a mature coding sequence of SEQ ID NO: 2, wherein SEQ ID NO: 2 comprises at least one mutation encoding at least an amino acid substitution selected from the group P469A, P469C, P469D, P469F, P469G, P469H, P469I, P469K, P469L, P469M, P469N, P469Q, P469R, P469S, P469T, P469V, P469W, and P469Y, and optionally wherein SEQ ID NO: 2 comprises at least one further mutation encoding an amino acid substitution I204F, P304S, P377A, P466T, and / or P477A wherein the amino acid substitutions are defined with reference to SEQ ID NO: 1, wherein the polypeptide has less than 70% residual activity on acetyl-AlaAlaPro-paranitroaniline (Ac-AAP-pNA) as a substrate after the polypeptide has been kept at a temperature of 65°C for 15 min.