Substrates and Inhibitors of SAMHD1

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• SAMHD1 is a deoxynucleoside triphosphate (dNTP) hydrolase with implications in antiviral and anticancer therapies.
• Understanding SAMHD1's substrate specificity is crucial for predicting the efficacy and metabolism of nucleoside-based drugs.

Purpose of the Study:

• To investigate the impact of 2' sugar moiety substitutions on nucleotide substrate recognition and hydrolysis by SAMHD1.
• To elucidate the mechanisms underlying SAMHD1's stereoselective substrate specificity and identify novel inhibitory mechanisms.

Main Methods:

• Enzymatic assays were performed to evaluate the hydrolysis of various modified nucleoside-5'-triphosphates by SAMHD1.
• Computational modeling was employed to understand the structural basis of substrate binding and inhibition.
• Stereochemical analysis of 2' sugar substitutions was used to determine nucleotide substrate specificity.

Main Results:

• SAMHD1 exclusively accepts dNTPs with a (2'R)-2'-H configuration, excluding (2'R)-2'-F and (2'R)-2'-OH analogs due to steric hindrance.
• Arabinose ((2'S)-2'-OH) nucleoside-5'-triphosphates are accepted and hydrolyzed by SAMHD1.
• The SMDU-TP analog, featuring a (2'S)-2'-methyl sugar moiety, inhibits SAMHD1 activity by clashing with residue Y374 and impeding necessary conformational changes for hydrolysis.

Conclusions:

• This study reveals critical insights into the stereoselective substrate specificity of SAMHD1's dNTPase activity.
• A novel inhibitory mechanism involving steric hindrance and blocked conformational changes was identified for SAMHD1.
• The findings are vital for assessing the in vivo hydrolysis of FDA-approved nucleoside analogs by SAMHD1.