Tmt1b, formerly known as METTL7B, is a methyltransferase. It has been associated with alkyl thiol methyltransferase activity in the liver, and might act on protein substrates as well as small molecule alkyl thiol substrates like hydrogen sulfide [2]. Tmt1b is localized to the stacked Golgi, endoplasmic reticulum, and lipid droplets, and is upregulated in various cancer types including lung cancer, gliomas, and leukemia, suggesting its potential oncogenic role [1].

Despite evidence of its activity on certain substrates, its normal physiological role remains poorly characterized. Animal models, like those used to study TMT1A's conserved ability to methylate thiol-based histone deacetylase inhibitors, may be useful in elucidating Tmt1b's role in humans, given that Tmt1b was not found in chicken or zebrafish [3,4]. Also, in cancer cells, Tmt1b (METTL7B) and CD274 (PD-L1) were found to be mutually exclusively expressed at either the mRNA or protein level, with METTL7B negatively regulating PD-L1 expression [5].

In summary, Tmt1b is a methyltransferase with potential roles in alkyl thiol methylation and cancer-related processes. Although its physiological function is not fully understood, research using animal models and studies on its expression in cancer cells are providing insights into its role in normal and disease conditions, especially in cancer.