1H, 13C, and 15N Backbone assignments of the human brain and acute leukemia cytoplasmic (BAALC) protein

Abstract

The brain and acute leukemia cytoplasmic (BAALC; UniProt entry Q8WXS3) is a 180-residue-long human protein having six known isoforms. BAALC is expressed in either hematopoietic or neuroectodermal cells and its specific function is still to be revealed. However, as a presumably membrane-anchored protein at the cytoplasmic side it is speculated that BAALC exerts its function at the postsynaptic densities of certain neurons and might play a role in developing cytogenetically normal acute myeloid leukemia (CN-AML) when it is highly overexpressed by myeloid or lymphoid progenitor cells. In order to better understand the physiological role of BAALC and to provide the basis for a further molecular characterization of BAALC, we report here the ¹H, ¹³C, and ¹⁵N resonance assignments for the backbone nuclei of its longest hematopoietic isoform (isoform 1). In addition, we present a ¹H^N and ¹⁵N^H chemical shift comparison of BAALC with its shortest, neuroectodermal isoform (isoform 6) which shows only minor changes in the ¹H and ¹⁵N chemical shifts.

Keywords: Brain and acute leukemia cytoplasmic protein (BAALC); Heteronuclear NMR; Intrinsically disordered protein (IDP); Neuroectodermal and hematopoietic cell function; Resonance assignments.

Fig. 1

Sequence alignment of BAALC from selected species. First line is the longest human isoform 1 (l.if.), while all other lines are isoform 2 (s.if.). The last line that indicates the conservation: Asterisks = fully conserved; numbers are the occasions of the most frequent residue out of seven isoform 2 cases

Fig. 2

[¹H, ¹⁵N]-HSQC spectrum of ¹⁵N-labelled BAALC at pH 6.5, 283 K. Assignments for backbone amides are annotated. Non-degenerate protons of the side chain amino groups are connected by a shaded line. Figure prepared using Sparky (T. D. Goddard and D. G. Kneller, SPARKY 3, University of California, San Francisco)

Fig. 3

A IUPred2A prediction of BAALC indicating the disordered nature of this protein. The residue-specific IUPred2A score for BAALC is indicated as solid line. Values higher than the cut-off (0.5) indicate disordered segments, lower values predict structured regions. B The sequence specific secondary structure propensity (SSP) scores are presented (open circles). Values below 0 represent β-structure propensity. Helical propensity is indicated by positive values. At a given residue a SSP score of 1 or − 1 reflects fully formed α- or β-structure, respectively. The SSP script was used with the default setup and, as recommended for disordered proteins, only C^α, C^β and H^α chemical shift were applied

Fig. 4

Combined ¹H^N and ¹⁵N^H chemical shift comparison of BAALC isoform 1 and 6 based on [¹H, ¹⁵N]-HSQC spectra recorded at pH 6.5, 283 K. Resonance shift changes are minor (less than 0.1 ppm) except that for residue 53, which is the penultimate residue of isoform 6. Note, residue 54 having the largest change is not shown as these represent different types. Combined chemical shift is given by Δδ = [(Δδ²_HN + (Δδ_N/6.5)²)]^½ according to (Mulder et al. 1999)