The prognostic significance of serum XCL1 concentration in patients with acute lymphoblastic leukemia: a pilot study

There is no information about XCL1 in patients with acute lymphoblastic leukemia (ALL). The objective of this study was to correlate the serum levels of XCL1 and survival in ALL patients. Only ALL patients older than 12 months were considered to participate. Serum XCL1 was measured at diagnosis, end of remission induction, and end of consolidation. Thirty-three ALL patients with median age of 21 years (1-78) were included. Higher XCL1 level (above 50 pg/mL) at ALL diagnosis correlated with higher survival (p = 0.038), whereas XCL1 level at end of induction and consolidation had no significant correlation. Concerning the behavior of serum XCL1 during treatment, higher survival at 5 years was observed in the group with progressively decreased levels of XCL1 (70%) than those with progressively increasing (29%) or no detectable XCL1 (14%). In conclusion, higher serum XCL1 levels at diagnosis and their progressive decline throughout chemotherapy could be correlated with higher survival.

Structural and agonist properties of XCL2, the other member of the C-chemokine subfamily

Known for its unusual metamorphic native state structure, XCL1 has been the focus of most efforts to elucidate the structural, functional, and physiological properties of chemokines in the C subfamily. By comparison, its closely related paralog XCL2 remains virtually uncharacterized. Based on the importance of the chemokine N-terminus in receptor activation, it was hypothesized that two amino acid differences in XCL2 would alter its agonist activity relative to XCL1 for their shared receptor XCR1. This present study reveals several properties of XCL2 that were unexamined until now. Structurally, XCL1 and XCL2 are very similar, exchanging between the monomeric chemokine fold and an unrelated dimeric state under physiological NaCl and temperature conditions. Ca(2+) flux, chemotaxis, and heparin binding assays showed that the monomer form of XCL2 is responsible for G protein-coupled receptor activation while the dimeric form is important for GAG binding. Despite their high structural similarity, XCL2 displays a slightly higher affinity for heparin than XCL1. Because their in vitro functional profiles are virtually identical, distinct physiological roles for XCL1 and XCL2 are probably encoded at the level of expression.

Structural gymnastics of multifunctional metamorphic proteins

The classic structure-function paradigm holds that a protein exhibits a single well-defined native state that gives rise to its biological function. Nonetheless, over the past few decades, numerous examples of proteins exhibiting biological function arising from multiple structural states of varying disorder have been identified. Most recently, several examples of 'metamorphic proteins', able to interconvert between vastly different native-like topologies under physiological conditions, have been characterised with multiple functions. In this review, we look at the concept of protein metamorphosis in relation to the current understanding of the protein structure-function landscape. Although structural dynamism observed for metamorphic proteins provides a novel source of functional versatility, the dynamic nature of the metamorphic proteins generally makes them difficult to identify and probe using conventional protein structure determination methods. However, as the existence of metamorphic proteins has now been established and techniques enabling the analysis of multiple protein conformers are improving, it is likely that this class will continue to grow in number.