New studies about the insertion mechanism of Thymosin α1 in negative regions of model membranes as starting point of the bioactivity

Abstract

Thymosin α1 is a peptidic hormone already used in the therapy of several diseases. Until now, the description of the precise receptor and mechanism for its action still remains elusive. The interaction of Thymosin α1, which is unstructured in water solution, has been recently studied in sodium dodecylsulphate micellar systems and it was reported that Thymosin α1 inserts in micelle assuming a conformation with two tracts of helix with a structural break in between. An investigation of its interaction both with micelles of dodecylphosphocholine alone and with mixed dodecylphosphocholine-sodium dodecylsulphate micelles is here reported. In these environments the results indicate that Thymosin α1 in phospholipidic membrane exposing choline polar heads interacts by aspecific modality and, oppositely, in the mixed dodecylphosphocholine-sodium dodecylsulphate micelles an insertion in the micellar hydrophobic region conformationally similar to that found in sodium dodecylsulphate micelles occurs. In presence of mixed micelles the insertion and structuration occur in preferred regions when the membrane models are negatively charged. From the point of view of the mechanism of action, insertion its N terminus in negative regions of membrane led to hypothesize that this process would be similar to a binding to phosphatidylserine exposed like in apoptotic cells. Thymosin α1 when inserted may interact with nearby proteins and/or receptors acting as effector and causing a biological signaling cascade. The recent attention to the phosphatidylserine exposure in cells may enforce the interest for these findings.

Thymosin α1 represents a potential potent single-molecule-based therapy for cystic fibrosis

“…Thymosin alpha 1 (Tα1) is a naturally occurring polypeptide of 28 amino acids 17 , whose mechanism of action as an immune modulator presumably involves an ability to signal through innate immune receptors 18 , activated by dynamic association with membrane phosphatidylserine 19 . Tα1 (ZADAXIN ® ) is used worldwide as an immunomodulator in viral infections, immunodeficiencies, malignancies, and HIV/AIDS 20 .…”

Thymosin α1 Interacts with Hyaluronic Acid Electrostatically by Its Terminal Sequence LKEKK

“…After the complete assignments obtained on the basis of previous work on Tα1 [ 25 , 26 , 27 , 28 , 29 , 30 ] the preliminary analysis of the 15 N chemical shift by the algorithm of Wishart and Sykes corrected for short peptides [ 57 ] confirmed values characteristic of the presence of a short tract in helical conformation from residue Ser1 to Val5 in presence HA at 0.4% ( w / w ) concentration ( Figure 3 c).…”

“…The individual and sequential assignments of Tα1 were obtained by TOCSY and NOESY experiments with different mixing times as reported in the Materials and Methods. Heteronuclear 2D NMR spectra ( 15 N-HSQC) at natural abundance ( Figure 3 a) were used to overcome ambiguities and complete the assignments of the homonuclear 2D NMR spectra using the previously reported results [ 27 , 28 , 29 , 30 ]. The appearance of NOEs in the NH–NH region of the NOESY spectra reported in Figure 3 b allowed us to carry out the sequential assignment of the peptide; intense NH–NH (i, i + 1) NOEs strongly suggest the presence of a helical conformation [ 56 ].…”

“…Recent studies with model membranes indicate that Tα1, unstructured in water solution, assumes tracts of helical conformation in structuring solvents like trifluoroethanol [ 25 , 26 ]. Interestingly, it assumes a conformation with two helical domains and inserts the first 5 residues of the N -terminal helix [ 27 , 28 , 29 , 30 ] in negative membranes models and particularly upon the phosphatidylserine (PS) exposure as found in several pathologies and apoptosis [ 31 ].…”

Thymosin α1 Interacts with Exposed Phosphatidylserine in Membrane Models and in Cells and Uses Serum Albumin as a Carrier

“…The interaction of Tα1 with trifluoroethanol (TFE) , and negative micelles by SDS has recently been studied by nuclear magnetic resonance (NMR) spectroscopy showing two tracts of mainly 3 10 -helical conformation with a structural break between them (BMRB entry 19901 and Protein Data Bank entry 2MNQ). From these previous studies − of Tα1 in micelles of DPC in the presence of SDS, it has been hypothesized that Tα1 may interact with phospholipidic membrane regions showing polar heads with a net negative charge such as the system formed by phosphatidylcholine (PC) in the presence of negative component phosphatidylserine (PS).…”