Polypeptide polycationic

Haselmann, K. F. Jorgensen, T. J. D. Budnik, B. A. Jensen, F Zubarev, R. A. Electron capture dissociation of weakly bound polypeptide polycationic complexes. Rapid Common. Mass Spectrom 2002, 16, 2260-2265. 

Branched polypeptides developed in our laboratory with the general formula poly[Lys(Xi-DL-Ala )] (XAK), where i < I, m approx 3, and X represents the side-chain terminal residue (6-8) will be used (Fig. 1) to illustrate the methods utilized for different conjugation procedures. Depending on the nature of the amino acidX, polypeptides exhibit polycationic (e.g., poly[Lys(DL-Ala )], poly[Lys(Ser,-DL-Ala )], amphoteric (e.g., poly[Lys(Glu,-DL-Ala, or polyanionic (e.g., poly[Lys(Ac-Glu,-DL-Ala )]) character under physiological conditions (pH 7.3 in 0.15 M NaCl). 

Amino Acid Sequence. We have already pointed out that because of polycationic properties and possibly because histones may, like antibodies, have a common polypeptide segment, histone separation is extremely difficult by conventional methods. However, histones have been divided into three major categories referred to as arginine-rich, moderately lysine-rich, and very lysine-rich. 

The insertion of the polymers into monolayers was also studied by comparing the compression isotherms. Lipid monolayers were formed on 0. IM sodium acetate buffer (pH 7.4) subphase in the presence or absence of polymers in a rectangular Teflon cuvette of 28.5 cm x 17.5 cm. After 10 min stabilisation period, a Teflon barrier compressed the monolayer at a speed of 4.2 cm/min and surface pressure vs. area (tc vs. A) isotherms were recorded. Data are summarised in Table 11. We observed no changes in the shape of area vs. pressure curves obtained in the presence of polymers in the subphase (data not shown), but polymers induced an expansion of the monolayer. These changes were detected at various surface pressures (10, 20, 30, 40 and 50 mN/m) and are expressed as area/molecule of phospholipid values (Table 2). These values indicate significant differences in the interaction of polycationic and amphoteric/polyanionic polypeptides. Marked expansion of DPPC monolayer occurred in the presence of SAK or AK (AA=0.23-0.51), while EAK and Ac-EAK initiated only moderate changes in this parameter (AA=0.01-0.13). The effect of polylysine and OAK was negligible (AA=0.01-0.03). 

Taken together data obtained indicate that the effect of polymeric polypeptides on DPPC (95/5, 80/20 mol/mol) liposomes saturated with ANS was strongly influenced by the PG content of the bilayer. In both liposome compositions polycationic OAK with a- and e-amino groups caused the highest increase of polarisation. Similar effect was observed at Tamino group, but at T>Tc temperatures its behaviour was similar to that observed for AK, SAK, EAK or Ac-EAK polypeptides. 

P-0.4 values were calculated for liposomes containing 5% PG at Tfluid crystalline phase transition (Tc(dppc) 40.5°C) (Fig.7a). P values of DPH after incubation with buffer or polypeptide solutions were almost the same. Among polycationic compounds the highest - but moderate increase in polarisation (AP 0.04) was observed in the presence of polylysine in the whole temperature range tested. This polypeptide initiated the highest increase (+1°C) of T which is indicative for interaction. 

Polylysine had the most pronounced rigidifying effect (AP 0.05) (Fig.7b). Polycationic branched polypeptides (AK, SAK, OAK) had moderate (AP=0.01-0.04), while amphoteric (EAK) and polyanionic (Ac-EAK) derivatives had no influence on polarisation. Presence of polycationic polypeptides increased the transition temperature (ATc +0.5-1.3 C) and widened the temperature range of the phase transition, indicating that penetration of polymeric polypeptides into phospholipid bilayers resulted in increased distance of phospholipid molecules. 

The surface properties at the air/water interface and the interaction of polycationic (polylysine, AK, SAK, OAK), amphoteric (EAK) and polyanionic (Ac-EAK) polypeptides with mono- and bilayers composed of DPPC or DPPC/PG was investigated. 

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