SMBHs are almost ubiquitous in galaxies' nuclei in the local and in the high-redshift Universe. However, the formation and growth processes that lead to the such massive objects in relatively short timescales are still unclear. A crucial role in accelerating their evolution may be played by the surrounding environment: large quantities of gas and higher merger rates are key to understand how their growth occurs. Protoclusters of galaxies, the precursors of today's galaxy clusters, represent the perfect laboratories to investigate this effect at high redshift. The hunt for the SMBHs population in protoclusters and its characterization requires a multi-wavelength effort to obtain a complete census: in this perspective the X-rays represent the best channel to investigate the AGN activity, even in the most obscured conditions. In this talk, I will present recent deep (>200ks) Chandra observations targeting three protoclusters at z ~ 2-3, that host enormous Ly? nebulae. I will discuss the spectral properties of the detected AGN as well as the effects of overdense environment on the growth of SMBHs. In particular, I will show the fraction of AGN and the X-ray luminosity functions of the protoclusters, which are significantly larger (1 - 2 dex!) than those of their local counterparts. Finally, I will present new results on how the enhancement of SMBHs in overdense environments (x10 larger than SMGs) suggests that protoclusters are indeed optimal sites for promoting their growth.