Human serum and milk albumins are metal‐dependent DNases

Abstract

It is known that that human serum albumin (HSA) and alpha-lactalbumin (LA) possess DNA-binding sites. Electrophoretically homogeneous HSA and LA containing no canonical enzymes were isolated from human sera and milk. Here we have analyzed for the first time the possibility of DNA hydrolysis by these proteins. It was shown that HSA possesses metal-dependent DNase activity, while LA cannot hydrolyze DNA. Several rigid criteria have been applied to show that DNase activity is an intrinsic property of HSA from human sera and milk. HSA preparations were inactive after their dialysis against EDTA or in the presence of EDTA, but were activated after addition of several external metal ions: Mn > Mg > Ca . The best activation of HSA preparations was observed in the presence of two metal ions: Mg +Ca > Mn + Ca ≥ Mn + Mg . In contrast to DNases having only one pH optimum, HSA preparations demonstrated two well-pronounced optima at pH 5.7-5.9 and 6.9-7.1 as well as a weak optimum at pH 8.4-8.6. These results demonstrate the diversity of HSA in the DNA hydrolysis at various pHs and in activation by various metal cofactors. Possible reasons for the diversity of HSA preparations are discussed. © 2018 IUBMB Life, 70(6):501-510, 2018.

Serum Albumin: A Multifaced Enzyme

“…Moreover, it shows DNA- and RNA-hydrolyzing activity, and anti-oxidant properties [ 4 , 75 , 76 , 77 , 78 , 79 ]. In addition, HSA displays heme-based globin-like (pseudo-)enzymatic properties including catalase, peroxidase, and NO/O 2 detoxification actions [ 4 , 11 , 17 , 22 ].…”

“…HSA has also been suggested to display the esterase activity towards nucleic acids. DNase activity has been hypothesized to occur at NTS and MBS since it appears to be metal-dependent [ 10 , 11 ] RNase activity has been attributed to Lys195-Lys199 and Lys541-Lys545 dyads since post-translation modifications of these residues (i.e., glycation, N -homocysteinylation, and N -phosphorylation) inhibit the RNA hydrolysis [ 10 , 102 , 103 , 127 ].…”

“…Human serum albumin (HSA) is the most abundant protein in plasma, representing the main determinant of the oncotic pressure and of fluid distribution between body compartments [ 1 , 2 , 3 , 4 , 5 , 6 ]. Moreover, HSA is the main carrier of endogenous and exogenous ligands, including fatty acids (FAs), nucleic acids, hormones, metals, toxins, and drugs, accounts for most of the pro- and anti-oxidant capacity of plasma, and displays (pseudo-)enzymatic properties [ 4 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. Furthermore, HSA plays a pivotal role in heme scavenging acting as a depot and a carrier of the macrocycle; in fact, HSA transfers the macrocycle from high- and low- density lipoproteins (i.e., HDL and LDL, respectively) to hemopexin.…”

Serum albumin and nucleic acids biodistribution: From molecular aspects to biotechnological applications

“…Since no crystal structures are available, NA recognition by HSA has been derived from spectroscopic, functional, and molecular modeling studies. 3,86,87,120 Values of the dissociation equilibrium constant (i.e., K d ) for calf-thymus DNA binding to HSA are 2.2 Â 10 À6 M and 1.6 Â 10 À5 M (at pH 6.5 and 25.0 C),…”

“…The Cu 2+ ion bound to the highly accessible NTS site and the Zn 2+ or Mn 2+ ions bound to MBS both favor the accommodation of DNA by coordinating a water molecule and interacting with the phosphate group. 120 Synthetic NAs bind to HSA at two sites (named first and second, respectively) with K d ranging from micromolar to nanomolar values. Interestingly, K d values increase with the oligonucleotide length reaching a plateau at n ≥ 5 (n, number of nucleotides) for single and doublestranded olideoxyribonucleotides (ODN) (Table S1) and at n ≥ 4 for single-stranded ribooligonucleotides (Ribo-ON) (Table S2).…”