Study On The Protection Effect Of Soybean PM1 Protein And Its N-terminal Peptide On Lipidosome And Its Mechanism

Low temperature is one of the major abiotic factors that impedes plant growth and limits crop yield and geographical distribution.Many plants have developed physiological mechanisms to adapt to the low temperature environment in long period of evolution.Many researches have shown the close relationship between the expression of LEA proteins and the cold resistance of plant.LEA proteins can be divided into 6~7 groups according to the feature of their sequences.The PM1 protein of soybean belongs to the fourth group of LEA;researches have shown that PM1 protein can protect the membranein under drought condition.But the mechanism of PM1 protein protected membrane still unclear.Two kinds of liposomes were used in this study,one was made up of POPC,another was made up of EPG and POPC.Turbidity assay,dynamic light scattering and phase contrast microscopy were used to detect the protection of PM1 and its peptide fragments on liposomes under freeze-thaw.Under freeze-thaw treatment turbidity of POPC liposome and POPC:EPG liposome increased from 0.3 and 0.2 to 0.8,the size of some liposomes increased from 130 nm to 800 nm,and a large aggregation of liposomes was observed under a microscope.After adding PM1 and PM1-N protein(0.8 mg / m L)to the liposomes,the turbidity of the two liposomes did not significant change in particle size and microscope results neither.Only PM1 and PM1-N protein could maintain the stability of liposomes and prevent aggregation of liposomes under freeze-thaw.The mobility of the lipid molecule was measured by using the dye merocyanine 450.When the POPC liposome was treated with liquid nitrogen and-20?,MC-540 fluorescence values were reduced from 8500 and 9300 to 6000,PM1 and PM1-N proteins could inhibit the decrease of fluorescence intensity of MC-540.The fluorescence value of MC-540 was increased from 1600 to 2600 after POPC:EPG liposome treated with liquid nitrogen.Under-20 ? treatment,fluorescence of POPC:EPG liposome increased from 1600 to 2200.When PM1 and PM1-N proteins were added,the fluorescence values of the liposomes changed a little.And then,the effect of PM1 and its short peptides on the phase transition temperature of liposomes was determined by DSC(Differential Scanning Calorimetry).The phase transition temperature of POPC liposome and POPC:EPG liposome were 1.3? and 1.5?,respectively.When the PM1 protein and its short peptides were present in the liposomes,the phase transition temperature of the two liposomes did not change obviously.Circular dichroism(CD)and trypsin digestion were used to study the interaction between PM1 protein and liposomes.The CD spectra and degradation rates of the proteins did not change significantly in the presence of liposomes.The results confirmed that PM1 protein did not bind to the lipid bilayer.Based on above studies,we speculated that the PM1 protein attached to the phospholipid head by its N-terminal,and then filled around the liposome,protected the liposome by molecular shielding under freeze-thaw treatment.