Magnetic field dissipation via reconnection is a promising process for explaining the non-thermal signatures from a variety of relativistic astrophysical outflows, such as pulsar wind nebulae (PWNe) and jets of active galactic nuclei (AGN). In most relativistic astrophysical outflows reconnection proceeds in the so-called relativistic regime in which the Alfven velocity of the plasma approaches the speed of light. In contrast to PWNe, where the outflow is composed of relativistic pairs, in AGN jets the composition of the plasma is largely unknown. Our goal is to study the general properties of relativistic reconnection in the unexplored regime of plasmas with mixed particle composition. We focus on pair-proton plasmas, as they bridge the gap between the pair plasma and electron-proton plasma cases that have been extensively studied in the past. We perform a suite of 2D PIC simulations using the realistic proton-to-electron mass ratio (mi/me=1836) while varying three physical parameters, namely the plasma magnetization, the plasma temperature, and the pair multiplicity. We study, for the first time, the energy distributions of accelerated particles, the inflows and outflows of plasma in the reconnection region, and the energy partition between pairs, protons, and magnetic fields, as a function of the pair multiplicity in the regime where protons dominate the rest mass energy of the plasma. We finally discuss our results in the context of non-thermal emission from AGN jets.