Understanding how molecular diversity across long-range neural circuits governs brain function remains a central challenge in neuroscience. Here, we developed a projection-specific spatial proteomics approach and revealed robust presynaptic molecular divergence across six projection-defined pathways of the medial prefrontal cortex (mPFC), including efferent projections to the basolateral amygdala (BLA), nucleus accumbens (NAc), thalamus (Thal), hypothalamus (HT) and cortex (CTX), as well as the afferent projection from the BLA to the mPFC. Among these pathways, we identify BLTP2 (KIAA0100), a previously uncharacterized transmembrane protein, as highly enriched in the projection from the mPFC to the BLA. BLTP2 localizes to excitatory presynaptic terminals and is enriched at synapses that are activated during memory formation. Loss of BLTP2 impairs synaptic structure and transmission, and reduces activity-dependent remodelling, resulting in selective deficits in contextual fear memory, anxiety-related behavior, and social behavior. Mechanistically, BLTP2 promotes presynaptic assembly by recruiting Neurexin 1. These findings reveal projection-specific presynaptic molecular diversity and provide mechanistic insights into circuit-level vulnerabilities in neuropsychiatric disorders.