The invention concerns polypeptides of the general formula (I): A-(Xaa)n-Lys-X-Lys-B wherein: i) A is —NH2, NH3+, or NH-D (D is an acyl group being biotin or an alkyl chain (C2-C22)), H) B is H, O−OR1 or NR2R3 and R1, R2 and R3 independently either: H or an alkyl chain (C1-C24), iii) (Xaa)n is an amino acid chain including any amino acid natural or not, excluding arginine and lysine, iv) “n” is between 0-3, and v) X is either a chain of two any amino acids (Xaa1Xaa2) which may be the same or different, excluding arginine, lysine and excluding Xaa1Xaa2=Thr-Thr, Gly-His and Glu-His, or X is a spacer selected among beta-alanyl, 5-amino-valeroyl, 4-amino-cyclohexanoyl, 4-amino-butyroyl, 6-amino-caproyl and derivatives thereof. More particularly, the invention concerns polypeptides of formula (I) wherein “n” is 0 and with the formula: A-Lys-X-Lys-B; A, X and B being defined herein. Compositions containing at least one of said polypeptides and their use.