Involved in microtubule stabilization in many cell types, including neuronal cells (PubMed:9600916). Specifically has microtubule cold stabilizing activity (PubMed:9600916). Involved in dendrite morphogenesis and maintenance by regulating lysosomal trafficking via its interaction with TMEM106B (By similarity). Regulates KIF5A-mediated axonal cargo transport (By similarity). Regulates axonal growth during neuron polarization (PubMed:28521134). Interacts with calmodulin (via C-terminus); the interaction is dependent on Ca(2+) (PubMed:14516200). Interacts with TMEM106B (By similarity). Interacts with ZDHHC13 (via ANK repeats) (PubMed:26198635). Interacts with ZDHHC17 (via ANK repeats) (PubMed:26198635). Isoform 1 and isoform 2 associate with axonal microtubules in neurons (PubMed:16837464). Isoform 3 associates with microtubules in fibroblasts (PubMed:9600916). Localizes predominantly in the proximal part of the axon (By similarity). Preferentially is concentrated on a portion of the microtubule polymer in which tubulin is modified by detyrosination and acetylation and is also resistant to depolymerization induced by both nocodazole and cold (By similarity). In unpolarized neurons, localizes to the Golgi and to secretory vesicles accumulating transiently at the tips of a subset of neurites (By similarity). Following neuronal polarization and during axon outgrowth, accumulates in the axonal growth cone and subsequently localizes throughout the axon. Partially localizes to dendrites in mature neurons (By similarity). Comment: Additional isoforms seem to exist. Isoform 1 is specifically expressed in adult brain. Isoform 2 is predominantly expressed in embryonic brain; expression persists at low levels in the adult brain. Isoform 3 is expressed at high levels in lung and at lower levels in testis, heart, muscle and kidney (at protein level). Oligodendrocytes express a major isoform of 89 kDa (O-STOP). Astrocytes also express an isoform of 60 kDa (A-STOP). Isoform 2 is expressed in embryonic brain. Palmitoylated. Probably depalmitoylated by ABHD17A, ABHD17B and ABHD17C. During neuronal polarization, palmitoylation and depalmitoylation cycles regulate MAP6 shuttling between secretory vesicles and microtubules, and its polarized distribution in the axon. Mice are devoid of cold-stable microtubules and show no detectable defects in brain anatomy but show synaptic defects, with depleted synaptic vesicle pools and impaired synaptic plasticity, associated with severe behavioral disorders, including a disorganized activity with disruption of normal behavioral sequences and episodes of hyperlocomotion or apparent prostration, anxiety, severe social withdrawal and complete nurturing defects (PubMed:12231625). The behavioral defects are alleviated by long-term treatment with neuroleptics (PubMed:12231625). RNAi-mediated knockdown in brain at the 14.5 dpc stage disrupts proper neuron migration resulting in their accumulation in the ventricular and subventricular zones (PubMed:28521134). Produced by alternative promoter usage. Produced by alternative splicing of isoform 1. Produced by alternative promoter usage. Belongs to the STOP family.