Immunoglobulin-binding polypeptide

1. A polypeptide, that binds to a protein comprising an Fc region of an immunoglobulin, the polypeptide comprising the following amino acid sequence:

(SEQ ID NO: 47)

RFX 1 X 2 EQQNAFYEILHX 3 PNLTEEQRNX 4 FIQX 5 LX 6 X 7 X 8 PSVSREX 9 L

AEAX 10 X 11 LNDAQAPX 12

wherein X 1 is D, E, N, or Q;

X 2 is E or R;

X 3 is L, M, or I;

X 4 is A, E, F, R, Y, or W;

X 5 is D, E, H, I, L, Q, R, S, T, or V;

X 6 is H, I, or R;

X 7 is D, I, or R;

X 8 is D or E;

X 9 is I, L, or V;

X 10 is R or Q;

X 11 is H or R; and

X 12 is R, G, or K.

2. A polypeptide, that binds to a protein comprising an Fc region of an immunoglobulin, the polypeptide comprising the following amino acid sequence:

(SEQ ID NO: 48)

Z 1 Z 2 Z 3 RFX 1 X 2 EQQNAFYEILHX 3 PNLTEEQRNX 4 FIQX 5 LX 6 X 7 X 8 PSVS

REX 9 LAEAX 10 X 11 LNDAQAPX 12

wherein X 1 is D, E, N, or Q;

X 2 is E or R;

X 3 is L, M, or I;

X 4 is A, E, F, R, Y, or W;

X 5 is D, E, H, I, L, Q, R, S, T, or V;

X 6 is H, I, or R;

X 7 is D, I, or R;

X 8 is D or E;

X 9 is I, L, or V;

X 10 is R or Q;

X 11 is H or R;

X 12 is R, G, or K; and

Z 1 to Z 3 are each independently A, D, E, G, H, I, L, N, Q, R, S, T, V, or Y.

3. The polypeptide according to claim 1 ,

which has at least 90% sequence identity to one of the following amino acid sequences:

(SEQ ID No: 1)

ADNRFNREQQNAFYEILHLPNLTEEQRNAFIQSLRDDPSVSREILAEAR

RLNDAQAPG

and

(SEQ ID No: 2)

ADNRFNREQQNAFYEILHLPNLTEEQRNAFIQSLRDDPSVSREILAEAR

RLNDAQAPR.

4. The polypeptide according to claim 2 ,

which has at least 90% sequence identity to one of the following amino acid sequences:

(SEQ ID No: 1)

ADNRFNREQQNAFYEILHLPNLTEEQRNAFIQSLRDDPSVSREILAEAR

RLNDAQAPG

and

(SEQ ID No: 2)

ADNRFNREQQNAFYEILHLPNLTEEQRNAFIQSLRDDPSVSREILAEAR

RLNDAQAPR.