Mutant fragments of OspA and methods and uses relating thereto

A nucleic acid encoding a polypeptide comprising a first disulfide bond-stabilized C-terminal fragment of an outer surface protein A (OspA),

• wherein said first disulfide bond-stabilized C-terminal fragment is a hybrid C-terminal OspA fragment consisting of, from the N- to C-terminal direction, a fusion of a first and a second OspA portion from two different Borrelia strains, wherein said polypeptide induces an immune response protective against a Borrelia infection, and wherein:
• i) said first OspA portion consists of amino acids 125-176 or amino acids 126-175 of OspA from a Borrelia strain that is not the corresponding fragment of B. garinii, strain PBr OspA with SEQ ID NO:
• 8, wherein the numbering of amino acids is according to the numbering of corresponding amino acids of the full-length OspA of B. burgdoferi s.s., strain B31 with SEQ ID NO:
• 5;
• and
• ii) said second OspA portion consists of amino acids 176-274 or amino acids 177-274 of OspA from B. garinii, strain PBr (SEQ ID NO:
• 8), wherein the second OspA portion differs from the corresponding wild-type sequence of SEQ ID NO:
• 8 at least by
• a) substitution of the wild-type amino acid at position 183+/−3 of SEQ ID NO:
• 8 by a cysteine, and
• b) substitution of the wild-type amino acid at position 270+/−3 of SEQ ID NO:
• 8 by a cysteine,
• wherein a disulfide bond between the introduced cysteines is present.