The function of golli-MBP is less understood than that of the classic MBP. However, golli-MBP is believed to play an important role in various physiological activities such as the regulation of calcium (Ca) homeostasis especially in oligodendrocytes (OLs) and in T-cells ( Paez et al., 2007). The latter authors investigated this particular property of golli-MBP using fluorescent protein clones, cell lines and imaging techniques. It was revealed that when overexpressed in OL cell lines (N19), the golli proteins activate the elaboration of processes and sheets which retract rapidly following a depolarization with high potassium ions (K+). Simultaneously, a substantial augmentation of the concentration of intracellular Ca ions (Ca2+) was observed. Moreover, these events did not affect the viability of the cells. From the results obtained, Paez et al. (2007) suggested that golli proteins impact on Ca homeostasis by facilitating an entry of Ca2+ in the cells and not a discharge of Ca2+ from intracellular reserves. There are factors that are important for the achievement of golli protein function during Ca homeostasis. These include e.g. a myristoylation site at the C terminus of the golli domain, which is crucial for the activation of the Ca2+ influx by the golli proteins. Smith et al ( 2011) also reported that a deletion of the first 45 or 110 amino acids from the N-terminal myristoylation site of the J37 golli suppresses the activity of golli in calcium influx regulation in N19 OLGs. The same phenomenon was also observed during a single point mutation from Gly2to Ala2 of both J37 or BG21 golli. It is therefore acceptable to think that the regulation of Ca2+ homeostasis requires that the golli protein is bound to the plasma membrane as suggested by Paez et al. (2007).The investigation of the N19 processes using high-resolution spatiotemporal analysis showed elevated influx of local Ca2+ in locations with high concentration of golli. Study of the structure of golli showed that the protein possesses a binding site for monosialogangliosides whose deletion provoke a limited effect of Ca2+ in N19 cells.
Another study conducted by Paez et al. (2009) demonstrated that golli proteins modulate the concentration of Ca2+ in OLs via voltage-gated Ca channels. The uptake of voltage-gated Ca2+ oligodendrocyte progenitor cells (OPCs) during process extension and retraction is important for the development of the nervous system. The Usage a specific chelator for intracellular Ca2+ concentration ((BAPTA or Cd2+) to block the voltage-operated Ca2+ channels lead to a suppression of the capacity of the golli proteins to facilitate the process extension in a dose-dependent manner. The movement of OPCs from proliferative location to their final site in the brain is crucial for the development of the nervous system and involves extension/retraction processes where a Ca2+ uptake occur. The latter authors screened the implication of golli proteins in the OPC migration process using imaging technique and acute brain slice preparations from mice exhibiting a golli Knock out and golli J37 overexpression (JOE). It was revealed that the OPCs migration was facilitated by golli and was related with an augmentation of the activity of voltage operated Ca2+ channels. Moreover, during the movement, a significant low transient amplitude of Ca2+ and level of cell migration were seen in KO cells, whereas in JOE cells the pre-cited factors were substantially elevated. The results strongly suggest that golli proteins facilitate OPC migration through an increase of the level of oscillations associated with voltage-mediated Ca 2+.
During Ca homeostasis golli-MBP act to promote a Ca2+ uptake, whereas some classical MBP isoforms act to decrease Ca2+ uptake (Smith et al., 2011). It will then not be surprising that golli-MBP play a key role in the process of tooth mineralization.
Work cited
Paez, P. M. et al. "Increased Expression Of Golli Myelin Basic Proteins Enhances Calcium Influx Into Oligodendroglial Cells". Journal of Neuroscience 27.46 (2007): 12690-12699. Web.
Paez, P. M. et al. "Golli Myelin Basic Proteins Regulate Oligodendroglial Progenitor Cell Migration Through Voltage-Gated Ca2+ Influx". Journal of Neuroscience 29.20 (2009): 6663-6676. Web.
Smith, Graham S.T. et al. "Classical 18.5-And 21.5-Kda Isoforms Of Myelin Basic Protein Inhibit Calcium Influx Into Oligodendroglial Cells, In Contrast To Golli Isoforms". Journal of Neuroscience Research 89.4 (2011): 467-480. Web.
