Abstract
The neuroblastoma breakpoint family (NBPF) consists of 24 members that play an important role in neuroblastoma and other cancers. NBPF is an evolutionarily recent gene family that encodes several repeats of Olduvai domain and an abundant N-terminal region. The function and biochemical properties of both Olduvai domain and the N-terminal region remain enigmatic. Human NBPF15 encodes a 670 AA protein consisting of six clades of Olduvai domains. In this study, we synthesized and expressed full-length NBPF15, and purified a range of NBPF15 truncations which were analyzed using dynamic light scattering (DLS), superdex200 (S200), small-angle X-ray scattering (SAXS), far-UV circular dichroism (CD) spectroscopy, transmission electron microscope (TEM), and crystallography. We found that proteins containing both the N-terminal region and Olduvai domain are heterogeneous with multiple types of aggregates, and some of them underwent a liquid-to-solid phase transition, probably because of the entanglement within the N-terminal coiled-coil. Proteins that contain only the Olduvai domain are homogeneous extended monomers, and those with the conserved clade 1 (CON1) have manifested a tendency to crystallize. We suggest that the entanglements between the mosaic disorder-ordered segments in NBPF15 N terminus have triggered the multiple types of aggregates and phase transition of NBPF15 proteins, which could be associated with Olduvai-related cognitive dysfunction diseases.
Highlights
The neuroblastoma breakpoint family (NBPF) gene family mostly located in three regions of chromosome 1, namely, 1p36, 1p12, and 1q21
Expression of NBPF15 truncated proteins containing more than one Olduvai domain in the Escherichia coli system was a failed attempt (Supplementary Figure S1)
We found that successfully purified N-terminal-included proteins had more than one aggregated form, and were subdivided based on their aggregation properties
Summary
The NBPF gene family mostly located in three regions of chromosome 1, namely, 1p36, 1p12, and 1q21. The 1q21 region encompasses the largest cluster of NBPF genes, containing 11 NBPF members (from NBPF8 to NBPF18p) [2,3]. NBPF genes within this region had undergone evolutionary hyper-amplification [4]. NBPF7 plays a key role in α-catenin signaling, which regulates keratinocyte proliferation through functional interaction with NF-κB [7]. NBPF12 located in the proximal region of 1q21, and in a patient harboring an 889-kb microdeletion of this region, a delay in brain and body development was observed [8]. Despite the important roles of NBPF genes in physiological and pathological processes, the regulation of this gene family and their specific cellular functions and protein properties remain unknown
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