Fig. 1
Identification of natural CXCL10(1–73) and chemical synthesis of CXCL10(1–73). A Detection of relative levels of CXCL10(1–77) and CXCL10(1–73) by top down-tandem mass spectrometry indicates upregulation of CXCL10(1–73) in the synovial fluids of patients with RA. Data are shown as paired dots for each patient (n = 10). Relative levels of CXCL10(1–77) and CXCL10(1–73) (ratio of the intensity of the respective proteoform to the sum of intensities of both proteoforms) were compared using an unpaired t-test (*** p ≤ 0.001). B Four crucial aspects were defined to ensure a successful SPPS using Fmoc chemistry including the combined use of a hydrophilic resin, pseudoproline dipeptides and a dipeptide building block (indicated I-IV) at crucial positions and the continuous application of high quality solvents. The amino acid sequence of CXCL10(1–73) is depicted with the key positions where pseudoproline dipeptides and the dipeptide building block (bold and underlined) were incorporated. C The intensity of the detected ions with their respective mass/charge (m/z) ratio are displayed. The relative molecular mass (Mr) of CXCL10(1–73) was calculated with Bruker deconvolution software (inset on the right) based on the detected ions, i.e., the ions marked by [A] with 7 to 12 positive charges. The experimental Mr (8172.37) corresponded to the calculated theoretical Mr (8173.65)