---

Endostatin suppresses growth and progression of many tumors through binding to endothelial cell surface and extracellular matrix proteins like integrin, heparin, matrix metalloproteinase-2 and transglutaminase-2. There is an arginine rich motif on the surface of endostatin that is essential for binding to some of aforementioned proteins. It has been shown that a 27 amino acid peptide derived from amino terminal of endostatin responsible for its anti-angiogenic and anti-tumor activities and mutation of histidines bound to Zn significantly reduce its activity. In the present study, as regards the importance of Zn-binding loop in amino terminal and arginine 27 in carboxyl terminal, peptides corresponding to this region and a mutated variant including isoleusin 26 to arginine mutation synthesized and their structure and interaction with matrix metalloproteinase-2 and transglutaminase-2 analyzed using fluorescence spectroscopy, molecular dynamic and docking simulation techniques. This study aimed to analyze effect of placing two positively charged arginines on the structure and interaction of this fragment of endostatin. Results showed that placing two arginines close together in the carboxyl terminal of peptide increases fluctuations in total structure of peptide, alters Zn-binding loop in the amino terminal and makes binding energy of peptide to matrix metalloproteinase-2 and transglutaminase-2 more negative. It can be inferred that repulsion of two positively charged arginines in carboxyl terminal induces conformational changes in the whole structure and in the amino terminal loop region.

---

Electrostatic interaction between proteins and negatively charged polysaccharides leads to formation of stable colloidal system or causes complex coacervation. Therefore, in this study phase behavior of the mixtures of 0.4% milk proteins (sodium caseinate or whey protein isolate) with soluble fraction of tragacanth (up to 1%) or soluble fraction of Persian gum (up to 2%) as a function of pH (2–7) was investigated, in order to obtain appropriate protein:polysaccharide ratio to formation of soluble complexes in a wide range of pH. According to the results, the mixtures of sodium caseinate–soluble fraction of Persian gum, sodium caseinate–soluble fraction of tragacanth, whey protein isolate–soluble fraction of Persian gum and whey protein isolate–soluble fraction of tragacanth were soluble complexes at the whole pH range at the ratio of 0.4:0.6, 0.4:0.6, 0.4:2 and 0.4:1, respectively. Moreover, it was found that enhancement of total biopolymer concentration (at a same ratio) had no effect on the phase behavior of complexes. In addition, evaluation of the phase behavior of the mixture of milk proteins–alcohol-insoluble fraction of soluble part of native gums illustrated that both alcohol-insoluble and soluble fractions probably have impact on stability of complexes at mentioned ratios.